At the top of the list: Here is a blog dedicated to garden sheds. It's very nicely done with a number of inspirational photos. My favorite is the water wheel shed.
There are over 10K pictures on flickr.com - search for garden shed. It takes a while, but you can see just about any kind you would imagine. There are also a lot of good photos of storage and interior setups.
Gardensheds.com is a commercial site, but the photos are really nice. These are definately high-end and classy buildings.
Here are a few articles from Fine Homebuilding (my favorite magazine):
Popular Mechanics has a good on-line article with lots of detail on contructions techniques. I really like the cut-away diagram showing all the main points of shed construction:
Click on the image below for a good set of detailed shed plans by Southern Pine in their DIY section.
For you hardcore green builders, here is a site that shows in fine detail show to build a large shed out of pallets. I am not quite to the point of using pallets to build things, but I admire the design and technique shown here.