My current machine is a Dell XPS 13 Developer Edition, which ships with Ubuntu pre-installed.
Good battery life, excellent performance and nice size/weight - comparable to a 13" Macbook Air.
You'll ned a mini-DP to HDMI/DVI converter cable though.
FYI - all of this will cost you less than 10 bucks.
I have the 2014 edition, mine never gets uncomfortably hot, and I rarely hear the fan running. I routinely compile lots of code on it (C/C++ and some Java).
Mine is a 2013 edition (MLK / 2nd edt) w/ Core i5 3rd gen (I think).
I recently installed Fedora 20 on it with no problems. I except Ubuntu 14.04 works well too.
All the hardware works out of the box. As usually, the proprietary NVIDIA drivers gave me fits, so I've just uninstalled them for now. Battery life is still good, as usually the Intel chip is used, even with an external monitor connected (unlike a MacBook Pro).