Great Rack Building Sequence from Alistair Spence
Alistair just finished up this large porteur rack for his tandem and posted an extensive series of photos documenting the process. He also annotated many of them, giving a lot of hints along the way. It's recommended viewing if you are interested in rack building.
Some folks have been asking me in comments about tricks for making miters that aren't 90 degrees. Alistair covers this well starting at this photo.
Another flickr gallery that I've been enjoying comes from Mike Flanigan of ANT Bike. He has a lot of shots showing his homemade fixtures. I've been interested in making fixtures of my own and there is a lot to learn from these photos.