If it's a desktop, I won't comment, that's entirely up to you (maybe others have advice) - I haven't used a desktop regularly in at least a year. If it's a laptop, though, unless you work in a totally Windows-centric environment, a MacBook Pro is the only choice (even in a Windows shop, I'd consider it since you can dual boot and the hardware itself is really nice). Get one N-O-W.
Seriously - these things are freaking awesome, ever since I got one I can't imagine ever buying anything else. I've never met a person that bought one and didn't absolutely love it. First laptop I've ever had that didn't feel like a cheap plastic toy...
Go for a 15" matte screen, though - the bigger ones are too cumbersome, and the glossy screens just suck.