The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the +12 volt rail(s) can easily power a system with any single video card made. A high quality 700 to 750 watt power supply with sufficient current (amps) on the +12 volt rail(s) can power a system with two video cards operating in dual mode. There are a few exceptions like the new ATI Radeon HD 5XXX series cards which use less power due to their energy efficiency.
A high quality 500 to 550 watt psu will have a +12 volt rail rated at 40 amps. A high quality 700 to 750 watt psu will have a +12 volt rail rated at 60 amps.
In addition the power supply should be at least 80+ Bronze certified for energy efficiency. There are some models available which have achieved 80+ Silver and 80+ Gold Certifications.
Before purchasing a new psu you will need to decide whether you will eventually have a pc with one or two video cards.
Corsair, PC Power & Cooling, and Seasonic are some of the brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty. Some of the newer models come with a 7 year warranty. Lately we've been seeing a few other brands offering some high quality units. An example would be the Antec Earthwatts series which is a major improvement over Antec’s older psu’s like the Basiq models.
The Antec 300 is a very popular pc case with gamers on a tight budget. Ventilation, airflow, and cooling are excellent:
The Coolermaster is not good. See the little voltage switch on it? At best, it is an old, inefficient design.
The Corsair VX450 is good, and can handle that video card, but a VX550 would be better, as you'd be running it in a more efficient part of its range.
The Antec EA-500 that JohnnyLucky linked would be another good, inexpensive (but not "cheap") choice.
I just got done reading a pretty harsh criticism of OCZ PSUs, generally for cutting corners on component selection (like the capacitors). I have not yet seen a competent technical review of the Fatal1ty model.