Below are links to some great sites with lots of useful information.
American Hosta Society: If you really enjoy hostas you should join the AHS, a local Society or both. It is a great way to keep up to date on what is going on in the "World of Hostas" and to know when a local garden tour may be taking place.
Hosta Library: A great place to find most of the links listed below this and with lots of pictures of Hostas.
Don Rawson's Lists Book: Don has taken the time to put a lot of varieties into all different types of lists including size, color, leaf shape, themes and lots of other ways.
Hugo's Sports Page: Here is where you will find the most information regarding sports. If you do not know, a sport if when one variety gives of an eye or two that looks different from the parent, either a solid from a variegated, a variegated from a streaked, a variegated from a solid and a few other ways. Not through breeding flower to flower. I use this information to build my sports categories. These division(s) are then carefully propagated until a stable, new variety can be introduced.
Plants Galore: You can possibly get lost on this site if you like Hostas or any other plant. At some point I would like to incorporate the originators information this site contains.
Garden Web Hosta Forum: This is where I first got a real taste of what it meant to be a Hosta collector. Now with Facebook being so active it seems like this is not.