What video card will work?

i am looking to upgrade my video card, but it is very narrow because my psu is only 300W max and i have a slimline HP so i need smaller video card, what are some good video cards that i can get for what i have, i need something that i or you know will work. i play world of warcraft and i think my video card is holding me back cause i got a 2.8Ghz AMD Athlon X2 cpu and 4gb of RAM. any help would be awesome, thanks.|||Below is a link to some of the most powerful cards that fit in a slimline/low profile case. They don't require an extra PCI-E power cable, as they get all their power off the PCI-E buss. They only take up one slot, but are a tiny bit wider than normal.