Jennifer Marsman has built a very nice list of Windows 7 developer resources
. Of course, she had me at Code Pack (the very first item she lists as a matter of fact), but she carries on, drilling into both native and managed scenarios, covering libraries, SDKs, training materials, UX guidelines, samples, blogs - even Twitter handles!
There is a LOT of material out there and it's a little bit fragmented. This is a great post to help you find your way around. Remember, if you have a Windows app, it should be a Windows 7 app!