mechanical or rubber dome switch? this is your first decision.
in rubber dome switches its hard to beat the value of logitech. even microsoft makes a decent keyboard. find a keyboard in store and practice typing for feel. find one that is comfortable for you.
in mechanical switches most keyboards use cherry switches. figure out if you like a key letoff or not, a click sound or not and what sort of resistance you like and pick a keyboard that has that type of switch. some good brands are deck and das but there are others out there as well.
personally i love mechanical keyboards... but if you only wanted to spend $50 you best be looking at logitech rubber dome switch keyboards or microsoft keyboards which will get the job done on a budget.