I was in the same position some time ago. I wanted something cheap and small to shove in my backpack and carry to the uni library/ wherever. I wanted a keyboard and the potential to use it on some place other than the loo, so a tablet was out of the question.

I got a cheap Toshiba netbook (the NB500) put ubuntu on it along with 2gb of ram, and it works quite well. Linux is more than passably fast on it after a few tweaks, the battery life is good, and it has ran very reliably. I actually found myself using it at home instead of my windows laptop for non-demanding tasks (it multitasks libreoffice, firefox and pdf reader like a boss). By my reckoning, any cheap laptop/ netbook with a linux distro on it should serve you quite well, as long as you don't want to do anything too intensive.