If you are considering the GTX 960 and HD 7970, then don't consider the 750Ti unless you are just trying to spend as little as possible or don't have a strong PSU. The 960 and 7970 are well ahead of the 750Ti in terms of performance.
As for other cards of good performance you could consider the GTX 950, R9 280, or any number of other cards in that performance range.
You'll want to look a little further down in the legacy section for older cards. Then find the cards you're looking at and see what is in the same tier. Just try to stick to newer GPUs, older ones may no longer have driver support.
I am looking to build a pc for a friend, and I think I know what mobo and cpu I will get and I found a 750ti for £45 on Ebay, I'm not really sure about the Psu yet but I will probably upgrade it, should I go with the 750ti because I can out more money towards other things?