Some good 64bit background info (the next post will be about CLR and WOW64, promise!)
I plan to mix things up here a little bit, in that sometimes I'll talk about writing managed code to run on a 64bit box (both in 32bit and 64bit modes), sometimes I'll talk about how the CLR is implemented to make it work well on 64bit boxes, and sometimes I'll just talk about 64bit native code in general. I'll try to get some categories worked out to that effect...
But for now here's some good info on 64bit native stuff that I might well refer to in the future (the first four links are from Raymond Chen's wonderful blog):