One of the best ways to add verisimilitude, style, and flavor to your game is with invented languages and names. This is especially true in play-by-post and play-by-e-mail games: it's easier to type odd words than to say them (especially for those of us who are not actors or orators). And since e-mail and message-board games allow time to compose and refine written turns, you have the luxury of making sure you do it right before clicking that send button.
But how do you come up with the odd words? The hardest but most realistic way is to create your own language. A really good source for how to do that is Mark Rosenfelder's Language Construction Kit.
But you may be just as happy using a language someone else has invented. Here are a few good ones:
Okay, so the elvish and the Klingon are a little overused -- so what! A sprinkle here and there might be tasty.
Of course, you may be content just to have a few new names to give your characters and monsters. A random name generator may be just what you need -- and with a randomly generated name like "Cayzle," I am living witness to that!
For the orc-elf sea dogs out there, don't pass up these transaltion machines!
Edit [6 Jan 05]: I stumbled on a few more good places to find constructed languages: