Resources from for Photoshop
Straight from the Horses mouth - So to speak!

Photoshop CS3 Help Manual

Compare Photoshop CS4 Versions

Compare Photoshop CS4 Versions

Adobe Design center - THINK TANK AND DIALOG Center

Photoshop Help and Support

Photoshop CS4 Help from UK Site

K-12 Instructional Support Docs Lesson Plans and more

K-12 Online Community and documents

Adobe Education Home

Adobe Digital Schools Collection by Curricular area