iTunes 10.6 - iPhone no longer connects
The best way to resolve issues where a device is not connecting to iTunes is to uninstall and re-download iTunes. This has almost always worked for me and is also high on the list of things to do when troubleshooting this type of issue on Apple's website.

The list details are


Update iTunes
Restart iPhone
Recharge iPhone
Check USB connections
Restart Computer
Reinstall iTunes (Windows)
Resolve Software Conflicts


If all these steps fail Apple reccomends 

Make an appointment with a Genius or Contact Apple Technical Support