I use an ASUS UX301LA-DH71T. It's a 2560x1440 13.3" ultrabook with a Haswell i7 and can run up to 8 hours on battery. It's thin, light, small enough to be portable, and super-capable for development (8GB RAM, dual-SSD RAID, i7 CPU and the integrated GPU is faster than the discrete Radeon in my last laptop). I typically have it docked to a second screen, but use its keyboard for programming. I have no complaints. It even comes with a one-year accidental damage warranty from the manufacturer, which I've never heard of a manufacturer offering before.
If I cared less about having a decent GPU, I'd have also considered the Samsung ATIV Book 9 Plus (3200x1800 13" screen). I haven't looked at what's come out since the beginning of the year, but these two were the only non-Apple machines that met all my needs.
http://www.amazon.com/Zenbook-UX301LA-DH71T-Quad-HD-Display-...
If I cared less about having a decent GPU, I'd have also considered the Samsung ATIV Book 9 Plus (3200x1800 13" screen). I haven't looked at what's come out since the beginning of the year, but these two were the only non-Apple machines that met all my needs.