With the limited information you have given me I am going to suggest a 4850. They are ~$150 AR. Its a power hungry card so when sciggy asks for power supply, its for a good reason, as you may not be able to run it with your power supply. Also what resolution do you run your games in (very important)?
A 4850 most certainly isnt a power hungry card a decent psu with a 6 pin pcie connector will run it fine. Sure if you have a generic 350/400 Watt PSU it may struggle but to call it power hungry is wide of the mark. Your CPU may restrict a 4850 which basically means you wouldnt get the full potential out of the card, but you can always upgrade teh CPU later on if you feel the need. The 4670 would be worth considering also.
However as has been said this is all speculation until you let us know what you play and at what resolution. The Amps on the +12V rail of your PSU + or the make and model would be good also.