I use a Lenovo Thinkpad X220 that I purchased in August. The battery life with the 9-cell battery is downright amazing -- I just leave the charger at home now.

I use a Lenovo Thinkpad X220 that I purchased in August. The battery life with the 9-cell battery is downright amazing -- I just leave the charger at home now. The keyboard and screen are really nice too, although the widescreen aspect ratio takes a while to get used to. I also like the simple, matte black finish and the fairly utilitarian design that seems to have good ventilation and heat dissipation. Even the humble Core i5 in my build is also noticeably faster than any Core 2 laptop or desktop I've ever built or owned. My only regret now is not getting the convertible tablet version, since I underestimated how much I use wacom tablets, and having one built into the screen would be extremely convenient for me. However, what's best for me isn't best for you. If you use Linux and don't like tap to click or the Thinkpad trackpoint (the famous red pointing stick in the center of their keyboards), you might test drive the X220 before considering it, because the clickpad they put on these models will probably drive you nuts -- especially if you're used to the multitouch clickpads on Macbooks. Also, about the screen size. It's big enough to see what you're doing, but since it's a lot wider than it is tall, you should consider how the development software you use will work with it. I spend most of my time inside of VIM, so I just maximize the window and split everything vertically. With a nice bold 9 or 10pt font (96dpi), I still get about 100-110 columns of text in each vertical window and almost 50 lines, without having to resort to small fonts (I don't like squinting). So for me, this screen size and ratio actually works out very nicely. If you spend all of your time inside of Eclipse or Visual Studio though, the lack of screen height will probably cause some pain. Some people also report problems with noisy fans on this model. I haven't had this problem at all, but I intentionally avoided getting a soup'd up Core i7 configuration. That said, I would also suggest considering a Macbook Pro. They usually have excellent battery life and a fairly solid design.