I just went through this process... see the post here http://www.tomshardware.com/answers/id-2630166/system-v...
You really need to post you system specifications to get the "correct" help...
I finally choose the EVGA GeForce GTX 750 Ti FTW 2GB Gddr5 @ $139.00.
Reasoning:
1) Only pulls 65W and 85W w/ optional 6pin (adapter included).
2) May not use the 2GB, but it was cheap and I'll have it if I need it.
3) Gddr5 memory is "newer" technology and specifically for graphics.
4) Was only $75.00 +/- more than what I was originally thinking for a card.
5) Overclocked, it's a beast for the money.
The GTX 750 Ti "should" fit in most cases, check what you have. The GTX 750 Ti FTW is about Twice as long.