I am currently running the 8800GT 512MB (Gainward version) with an Antec True Power Trio 650w power supply, this supply is very good and is able to support the card with plenty of headroom.
As said before, if you want to play the latest games and are serious about it, do not even consider going less than an 8800 series or a HD2900 series video card.
I also must stress what
starjax has said, get a quality power supply, there's a reason cheap power supplies are cheap - and you don't want to find out! (Neither do I). Adding to the specs starjax has said to look at [plenty of watts, enough amps on +12V rail(s)], also look for the efficiency rating, try and get one that's at least 80% efficiency rating. There's plenty more to look for, but this is a good start.
Lastly, it's recommended to not purchase off eBay as you could get stung with a faulty product and/or high postage rates, especially if you have to return something to be replaced, you will probably have to fork out for
all the shipping. If you are looking to buy new products such as computer parts discussed in this thread, then purchase off a reputable dealer, preferably one who has a physical shop.
Recent Example:I recently purchased a whole bunch of parts and picked them all up local, except with the graphics card being posted from some 1000km away. (This was not through eBay). I went with them because:
a) The physical address was listed, and my brother lived near it. He told me it did in fact exist. The website was full of well-written information covering everything from warranties, to returns, to contact information and more.
b) Registered, insured postage by courier
was included in the listed price. Nice

So please, look up as much information as you can about products
and retailers, find out information on warranties, returns and postage fees for such.