Honestly, the GT520 is pretty lame in terms of graphics cards. It is probably the worst "display" based card out there.
Depending on what you want to do, I would highly recommend the Radeon 5670 or 6670. They are cheap and powerful; what more could you want?
Even the 5570 or the 6570 would be better, yet if its between those 2 and those 2 only, the 6450 is the best of the two.