I'm a final year student at university so unfortunately can't donate as much as I'd like to.
I do, however, have a monthly direct debit to charity of £15 a month and, whenever I come into some extra, unexpected or manifested money, I try to tithe 10%, usually into
http://www.kiva.org (fantastic microfinancing organisation - if you haven't heard of them, go take a look!).
I'll be graduating next summer and already have a grad job lined up, so hopefully can start to give back a little more then.