Just heard about this website on IHRS's Facebook. Its like webMD but for bunnies. I've just spent the last half hour perusing their database of rabbit health problems and tips to keep your bun healthy. I've already learned a lot in that short time and posted a nifty fact in the previous post.
Of course, no internet source can replace an experienced vet, so make sure to contact them if you are concerned about your fuzzy friend.