If I might chip in my two cents...
I'm currently working for a newly started production company, but I've been editing on Mac's for a while now.
Portable:
MacBook: If you don't want to spend a whole lot of money, go with a MacBook. I had and older Black MacBook a while back, 2 Gigs of RAM. It ran Final Cut Studio pretty well, at least well enough to keep up.
MacBook Pro: If you need to stay portable and money isn't much of an issue, go with the Pro. It's got plenty of power to run just about every program in Final Cut Studio 2. I currently have a MacBook Pro with 4 Gigs of RAM. Runs Final Cut Pro, Colors, Soundtrack, DVD Studio Pro, and After Effects pretty well. Gets a little warm at times though, so keep that in mind.
Desktops:
Mac Mini: If you have limited money, and don't mind non-portability, the mini would be best. I know it may seem to small or not powerful enough, but I was editing on them back when they were G4's! I'm sure it would be able to run Final Cut Express quite well, and should handle Pro, but may not be able to handle the likes of Motion or After Effects very well. It would probably be most comparable to a MacBook in terms of power.
iMac: If you prefer a desktop, but can't spend the big bucks for a Mac Pro, the iMac would suit you. It's nice and compact, and the 24" has quite the screen real estate. I ran Final Cut Studio and Logic Studio on one of these for a while and it help up like a champ. You can always add a second monitor if need be with a special adapter from Apple. I'd compare best to the MacBook Pro in terms of power.
Mac Pro: If money's not an issue, go for a Mac Pro. Most powerful Mac you can get. Plenty of room for expansion and it should be able to handle about any program you throw at it!
For all of the above computers, the more RAM the better. I'd suggest, like others have suggested, getting your RAM from NewEgg or Crucial, as you'll save a lot more getting it there and installing it yourself than you would if you ordered direct from Apple. If you get a Mac Pro you can also upgrade/add graphics cards and more hard drives (again I'd suggest NewEgg).
If you ever have any questions, feel free to PM me.
-Adam