A Dell Inspiron 560S desktop (700$-ish, few months old, 6 Gigs ram) with Windows 7 (which I love I really do, it just screams and works great), with 2 Viewsonic monitors (http://amzn.to/dqRAN1 very good, and I much prefer the more traditional aspect ratio, especially for dual monitors.).

Software-wise, it's Chrome + assorted browsers for testing, Notepad++ for editing code, Visio 2003 for wires. Paint.net for simple image stuff. Dropbox. Skype. That's about it.