These are books that have come in handy on many occasions in many settings. For tabletop, MUSH or MMORPG roleplaying you'll find yourself happy to have them around for inspiration or guidance.
The most important books on your shelf, for a specific game, will be any tabletop roleplaying rules that pertain to the setting. While the rules themselves don't apply the fluff text and orientation to the geography, politics, metaphysics, theology and history of a setting will always be a touchstone. It will also serve as information organized to expedite roleplaying that you can leap off from to research on the internet or in other books.
After this you may want to look for any "nonfiction" about a setting. Visual guides, encyclopedias, companions, lexicons, technical manuals and so on are quite valuable. While the MMORPGs themselves rarely seem to conform to the available information, which remains a sore point for roleplayers and genre fans, this is still fodder for you as a roleplayer. You and others will be inventing situations on the fly and characters and won't be, in your imaginations at least, restricted by mundane game design. The more a roleplayer knows about a setting, obviously, the more tools he has to improvise with.
Dropping setting appropriate references and terms, in passing and in moderation, also really enhances immersion. You can sound convincing as a crusty pirate or an ancient elf. Neither of those is a mean feat.
Character Names: While there are fine lists and generation programs on the internet, I tend to like having this kind of resource close to hand. Obviously, in any MMO, look to NPC names for ideas about how a culture names its people. If you can recognize a source-culture (Stygia = Ancient Egypt, Caldari = Finnish-Japanese) from the real world many of these name lists will be more useful. If not, play around with consonants or vowels on an existing example. Write down a list of examples , split them into prefix, middle (if any) and suffix syllables, and switch them around in different combinations. Or do both. Then say the name out loud and see if it sounds right to you. Try not to use sounds you don't hear elsewhere for it to sound right. Once you have a name that fits your character, that sounds both right and good, then you're ready.
The Everyone Everywhere List published by Magic & Tactics Unlimited (Now in a 3rd Edition but all are good). Cheap 8 1/2" by 11" pamphlet bound. I've used my first edition for ages now and it covers most common bases, historical and contemporary. Just a basic list of names broken down by culture.
Gary Gygax's Extraordinary Book of Names by Malcolm Bowers. A truly extraordinary, lives up to the billing, book that not only list names but describes how they come about. Broken down by cultural origin. Includes place names and spends a great deal of time on medieval England's naming practices (most common in fantasy games). Not only people but place names are covered. There are also sections on fantasy names for orcs, elves, demons and the like. Supercedes The Everyone Everywhere List by far in terms of scope but The List remains more handy for just snagging names on the fly because there's less there to dig through.
Character Naming Sourcebook by Sherrilyn Kenyon. A handy introduction on how to go about naming a character, from a writer's perspective, is followed by yet more name lists broken down by culture. These include the meanings of the name. This fat book mainly describes the names of modern cultures which makes it a third choice after the other two for me. However one neat tool, which is seems to be unintended, is the index that just list names in alphabetical order. Really want to see what's out there? Run a finger through the index and you'll have tons of ideas, especially for generic fantasy characters, without having to sort through separate cultural listings. You can always pick a name from the index then go look up the meaning if you want.
Character Brainstorming: Generally, when working on a concept, your best bet is really to understand the archetypes and stereotypes in the game already. Know the culture, know the character. It's up to you to decide how your character differs from the stereotype. More on this in "Thoughts on Character Creation." Really far out or bizarre or "powerful" (in RP you're really only as powerful as the game system or the other players let you be) or evil characters can be problematic. Subtle differences from archetypes are generally better received than more outrageous ones. Remember the character you create is the surface off of which other players see their character reflected. Too much distortion and you could be messing up someone else's good time and find yourself sidelined.
Building Believable Characters by Marc McCutcheon. If you want a quirk or a trait but are at a loss, pick through this one. It's really aimed mainly at fictional characters in the modern world but it's got some stuff you can use or be inspired by. Also useful are descriptive lists for character features. If you're writing a description, and often roleplayers will do this in a pose/emote to flesh it out with detail or in a biography, this will give you words to stock up on, Still, don't rely on this as much as the setting itself. Much of it simply won't apply or be appropriate.
Foreign Dialects: A Manual for Actors, Writers and Directors by Lewis Herman and Marguerite Shalett Herman. This one is real handy. In most settings some characters can talk with strange accents but, if you pay attention, you'll notice they're actually borrowing from real world dialects. Dwarves talk like Scots, right? Imperial Officers in Star Wars are British, upper class. With this book you can pick up some tricks of expression and learn what not to do. It's not a heavy study, really, because you're just trying to carry the general sense of it not be a master thespian! There's also a guide on American dialects but it's really too specialized for our purposes.
The Word Finder by J.J. Rodale. Need a word or a phrase? Give me a word. Horse, you say? I've got about 100 common words and phrases that could apply to a horse. From "startled" to "whinnies." Aha, now you have the power, padawan. This can actually be used to brainstorm on the fly too. It's not a thesaurus but a word finder. I don't need to tell you to get Roget's Super Thesaurus do I? I know you've already got that!
Storytelling: I can't stress this enough, your best bet is the source material for the setting. If you can get your hands on tabletop roleplaying books for the setting you should be set for story ideas. Pulling it off can be something else though. You might want to look at the previous entries "Spinning The Saga of Gresh'Maj" and "Lona's Event Guides for Dummies."
Gary Gygax's Insidiae Dan Cross. A pretentious name for a pretentious book. Still for all the lip-flapping and theorizing, Dan does offer a way to think about creating stories. How, when, who, why? What's the role of each NPC? What motivations does he have, what methods does he use? What's the context for a story in terms of politics or natural disaster or whatever else. It discusses how to organize a plot in detail. Maybe too much. However, if you need an idea fast and don't have anything more setting specific to work with, Insidiae can help.
The Big List of RPG Plots by John Ross. This actually does much the same thing as Insidiae but more efficiently and, better, it's free and downloadable. Ross went through all his old tabletop modules and distilled down common themes and plots. He also includes tools for mixing those plots up and making them work under "Handy Tip!" sidebars in the print-friendly version. If you're already comfortable with storytelling you can probably just make best use of The Big List without bothering with Insidiae. John spends much less time working through all the details of plot or possible permutations of NPC complications. He just lays out plot ideas, raw and to the point. Along with The Everyone Everywhere List, The Big List of RPG Plots is probably one of the most valuable things you can own, pound for pound and dollar for dollar.
Robin's Laws of Good Game Mastering by Robin Laws. Robin focuses more on the dynamics of how players think and how to sculpt an adventure or campaign to suit their tastes. He also shares tips for improvising situations when players go off the map and explains why that's sometimes to be celebrated. Much more useful a view of players, for our purposes, than Bartle's "Killer, Explorer, Achiever and Socializer" is Law's list of "The Power Gamer, The Butt-Kicker, The Tactician, The Specialist, The Method Actor, The Storyteller and The Casual Gamer." Know thyself, know thy players, and one cannot fail to deliver a good time. Apologies to Sun Tzu.
760 Patrons: Contacts, Mentors, Benefactors and Financiers by Bryan Steele. This book is written for the new Mongoose edition of the classic scifi tabletop RPG, Traveller. It's a list of NPCs. All kinds of NPCs. With simple modifications it works well in modern and most scifi settings. Need ideas for NPCs, contacts, foes, patrons, complications? Ding. Here ya go. Most, with some thought, could even inspire some stories just around them. They're vague enough to be resusable stereotypes but detailed just enough to show what kinds of direction the narrative might take. Combined with Insidiae's NPC personality/appearance tables you've got a fully fleshed individual. Might even work in some fantasy settings but the utility isn't as strong.
Nightmares of Mine by Kenneth Hite. The master of immersive storytelling, Kenneth Hite, wrote this book to help storytellers scare the bejesus out of their players in horror games like Call of Cthulhu or Kult. However much of it can apply to many games. Pacing, putting to together mysteries to be solved, setting and maintaining moods, screwing with player expectations (in a narrative sense) and other nice tricks are covered here.
Well, that's it for now. Will be back soon with more after a little break