I'd have gone for the macbook pro and external screen. I have a macbook and 20" screen, and it works brilliantly. Having a dedicated GPU in the laptop would make it just about the perfect setup.
If the work you do is critical and time consuming, the MBP/external display option is fine, but you absolutely want to have a premium back-up external hard drive.
I got a 15-inch MBP and a 20-inch Viewsonic Widescreen LCD monitor. I also bought 2GB RAM from NEW EGG, and it all costs me way less than 3grand. I mean, i'm a student so that helped, but i love the machine
laptop: 1800
monitor: 400
ram: 180
total: 2380
not bad
missed your post above. I doubt that Apple will release new iMac at Macworld, but i'd watch what Intel does.