I recently entered the National Collage Society's annual juried exhibit, and while my work was not chosen, there are a great variety of fantastic collages in the show. You should definitely check out the National Collage Society's 2010 26th Annual Juried Exhibit .
one of the pieces I entered: Dimensional Shift
I think you'll be inspired. They also sell catalogs of past exhibits, which are great; I have a couple of these, and look at them all the time. The newest one is an e-catalog.
The 2007 catalog is probably my favorite, but I don't think you could go wrong with any of them. They're also selling a calendar, which may be my Christmas gift to myself this year.
(Does anyone else ever get frustrated with how blogger won't let you put things where you want to, or is it just me? grrrr...)
When I feel the need to to feast my eyes on some really innovative paper art, I go to Upon a Fold.
Untitled work by Yoshinobu Myamoto
This site showcases amazing art made from paper- of every size and description you can imagine, from full-size cardboard bicycles to 3-D Christmas-tree cards. Often there are interviews with the artists, who are at least as fascinating as their work.
Book sculpture by Ryuta Iida
Cornfield by Ryuji Nakamura
These are just a few samples of what you'll find there; it's well worth checking out, for inspiration, or just for that, "HOW do they do that?" feeling.
Notpaper is also a site you won't want to miss. Each post is an interview with a featured collage artist. First of all, I had apparently grossly underestimated the number of collage artists in the world; secondly, I had no idea there were so many astoundingly good collage artists. A quick preview:
Portrait of a Three Legged Rabbit by Anne Marshall
And finally, what goes with paper like peanut butter goes with jelly? Glue, of course! To hold it all together (pun intended), I thought you might be interested to learn that there's a site dedicated to informing us of the proper glue to use for any circumstance. It's called This to That (Glue Advice), and it's so simple even my dog could use it! You just enter the two materials you want to glue together, click the button, and voila! The name of the best glue for bonding those materials (and a link to where you can buy it) will magically appear before you. (Don't worry, though; I don't let my dog use glue. She'd just glue the other two to the floor so she could have all the food.)