a high resolution is a must because it gives you more space to work. and make sure the keyboard layout and touchpad is of a high quality.
Thinkpads are nice, I would recommend a t430/t530 series or older with a 1080p res. The newest model did away with physical mouse buttons so i cannot recommend them.
High res isn't that great if you don't have the physical screen real estate to back it up. 1080p on a 13" screen without scaling is a little too small to work with effectively. From having seen my friends 14" Lenovo running at 1600x900 I'd say that's the max resolution for a 13-14" screen.
Macbooks are expensive, but Apple has excellent support and they are very high quality. If you can afford one and don't mind that it runs OSX instead of Windows it may be a good option.
My only Asus notebook was an old Eee netbook, but it served me very well and they're a pretty well-regarded manufacturer. (I gave it up because it was a tiny, underpowered netbook; it was great for the uses I had when I bought it, but by the time the charger broke I didn't need something quite so small anymore.)
*Turn Evil can now be cast on players. When used, it applies a small goatee and causes them to explain their diabolical plans while steepling their fingers.