27" i7 iMac with 8GB RAM, attached to a 30" Dell display (3007WFP). I switched about a month ago from a MacBook Pro (attached to the same Dell display), and it's phenomenal. It's the first setup I've ever had that actually feels fast enough to run everything I need (iTunes, Word, Excel, and Windows running in VirtualBox, along with a few instances each of iTerm, Chrome and Textmate) without skipping a beat.