My computer is an HP Slimline s5703w. I don't have much money and I'm looking for a card around $50. My friend got a GT 520 and he plays Diablo 3 on it, he says it runs fine and he hasn't seen any lag so far, but I'm not sure if Diablo 3 is a very demanding game. I may be buying a GT 520 soon if it's a good card, but I was looking through answers and noticed you guys don't seem to like that card. I also have no intentions on purchasing a new PSU because I don't have much money.
That is not a low profile graphic card. That is a full height graphic card that only uses one slot. A low profile card is like a "half height" card.
The following is picture of a low profile HIS H667FN1G Radeon HD 6670 which is currently selling for $90 after rebate @ Newegg.com. It is pictured with a full height bracket which can be replaced with a low profile bracket that is included with the video card.