If you don't need the newest and fastest, I recommend a ThinkPad X201 (upgrade the LCD to an AFFS one if you like a little DIY), or you can go really hard and get an X61.
Disagreed - the X220 top lid is flimsy and cracks easily, and the resolution is impressively terrible (WXGA! In 2015!). I do appreciate its moderate battery improvements, but I'd prefer an X201 in just about any other way.
EDIT: I almost forgot that the X220 front bezel warps outwards in even the slightest cast of sunlight on a nice day. It's pretty alarming when it's not expected.
Debian has worked great on both.