Thinkpad x220, 8gb RAM, i7, 2xSSD and run ArchLinux on it with Awesome WM, which is a really really great tiling window manager.
At home I plug into a 23in screen, mouse and keyboard, which works really well.
I also have a mid-2011 13" Macbook Air.
Since I've been doing iOS dev again, my X220 has been laying unused on a shelve, for around a year now. Shame on me, for its a very good machine.
http://www.crucial.com/store/partspecs.aspx?IMODULE=CT480M50...