Astromech.net
Detailed and illustrated R2 droid construction guide, with a discussion board.
Episode I Preview: R2-D2 Biography
Detailed biography of Star Wars' R2-D2, the lovable droid.
Italian R2D2 Builders Website
Drawings and resources for building a full size replica of R2D2 from Star Wars.
Star Wars: R2-D2 (Artoo-Detoo)
Luke Skywalker's trusty astromech droid. Profile from the official site.