A fun and fascinating resource for anyone interested in artificial languages is Mark Rosenfelder's Language Construction Kit [1]. And if you want to get extremely into it, I highly recommend Paine's Describing Morphosyntax for a detailed tour of diverse grammatical systems from across the world [2].
Oh yeah, I remember stumbling across the Language Construction Kit years and years ago. What sticks with me is that all the language stuff on his site was fascinating, and then I looked at the rest of his site and it turned out he was more or less batshit insane. I guess maybe that's not unusual for someone super-dedicated to a hobby.
David is a great guy. Before Dothraki and his other languages for hire, I exchanged emails with him and he gave me a bunch of advice on my own constructed languages.
Dittoed. I still exchange emails with him from time to time, and he still gives good advice. And is just an overall nice guy. If you ever get a chance to meet him in person, he's quite friendly.
[1] http://www.zompist.com/kit.html
[2] http://www.amazon.com/Describing-Morphosyntax-Guide-Field-Li...