Important XNA Links

XNA Creator's Club Forums
Shawn Hargreaves Blog - Microsoft Programmer for XNA
Focused Games
Ziggyware XNA News and Tutorials

A.I. (Artificial Intelligence)

Jean-Paul Van Waveren - Fuzzy Logic, Neural Network, Bot skill, much more....
Teachrose.com - Neural Network A.I.

Physics

Ageia PhysX
Havok Physics
XNA Physics - Sharky's 3D Collision Demo - Works with custom collision spheres
Rigid Body Sphere Collision Tutorial (Gamasutra membership required)

Graphics programming

--------

Game Porting

Cross Platform (Wikipedia)
Cross Platform Programming
Writing Cross Platform Software

Game Testing

Code Project (Advanced Unit Testing)
Agile Testing Blog
Black Box Testing (Wikipedia)
Black Box Software Testing
Black Box Testing Strategy
Black Box Unit Testing
Game Testing (Wikipedia)
Software Testing Glossary
White Box Testing (Wikipedia)
White Box Testing Strategy
Embedded Software Testing
Software QA and Testing Resource Center
Functional Testing VS. Non-Functional Testing
Unit Testing (Wikipedia)
QA and Software Testing