One with hi-res screen (1366 x 768) and Ion or accelerated graphics (for videos mainly), like the 311c, although I'm not a fan of a trackpad. My bro' has the Compaq rebranded model.
However, I'd rather recommend a CULV 13'' laptop, not much more expensive (well, £350), but a lot more powerful. Dell do some hybrids, basically a small laptop in a 11'' or 12'' chassis.