[Build Help] I need a good cost-efficient video card

I used to have a GTX 550 with my i7, but it stopped working and now I'm looking for a new one.

However, I don't run really demanding games (I.E. ports of new gen games, only exception might be Fallout 4, I wouldn't worry playing on low graphics though), and I just want another videocard with a reasonable price (the 550 used to run 99% of what I needed).

So, any suggestions? I've been thinking to buy a GTX 600-700 or equivalent for a good price, but I'm not really sure.