You can find out which of the coins are most profitable to mine by heading to:  http://www.wheretomine.com/   set your hash number at the top (most single GPU PC's manage 300-600khs) and order by 'Earnings' to get a rough idea how much you could mine in a day.

They're very, very rough estimates and also coins which are profitable today can be worth very little tomorrow, this is because difficulties increase, prices of coins can vary wildly, and some coins have bonus times when you can earn a lot more coins than usual.