There's some sort of feature list here:
http://www.winsupersite.com/showcase/winvista_feature_focus.asp
Not entirely exhaustive though. Some of my favourites are new networking stack built from the ground up with native IPv6 support - has shown up to 40x improvements in testing. New audio stack and controls on a per app basis rather than the non-sensical sliders we've had for years. The moving of boths this audio stack and the graphics into usermode mean that BSOD should be even less likely - a dodgy sound driver can't bring the system down anymore, for example. The Mobility Center should help laptop users leaving your network (something that was a real pain - offline files is part of that, and works much better now).
There are lots of 'little' things I've noticed and like a lot - Fast User Switching for domain logins, the ability to resize partitions on the fly using Computer Management...