Someone just started an Alpine thread, looks nice, he has a few issues though. Whether thats the install or the way the unit works, don't know, I gathered he's looking into solving it though if he can.
I have the Avic-Z2 and absolutely love it, plenty of features, there's also the Z1 which is the first generation and the recently released Z3 which is the third generation. The head units are identical, just different software on the harddrive so you can either just upgrade the maps by inserting a DVD or you can upgrade a Z1 or Z2 software as well as maps to a Z3 by downloading the image off avic411.com and have the newest generation that way.
Others have used the Kenwood 6120, 7120 and now theres a 8120 coming out. From the various posts, they appear to like them as much as the Avic users like theirs. I don't know much more about them other then they all appear to have similar feature sets as Brand B and C. Satellite, ipod, bluetooth, etc.. as well as being harddrive based so you don't have to swap out the navigation DVD for a CD when you want to listen to music which is a big plus for a navigation unit.
Anyway, you should be able to get plenty of feed back regarding each of the different types of head units; Alpine, Pioneer, Kenwood, Eclipse, etc.. here's some links to each so you can start checking on features.
Alpine Electronics of America, Inc.
Pioneer USA - Navigation
Kenwood - navigation
ECLIPSE Navigation System lineup | Fujitsu Ten