Moderately powerful card with low power consumption?

I'm looking to turn my rather ordinary desktop into a decently solid gaming computer. The processor, while a bit outdated, ought to hold up well enough to most games, I hope(X4 630). I can't make a gaming monster as is, but I at least hope to play some older games with mods and at least something to hold steady with the newer games until I do a full new system build.

I'll most definitely be replacing the PSU, which is way underpowered for graphic cards.

My question is, is there a moderately powerful card out there that is decent when it comes to power consumption? I was looking into the HD 7770 because it uses so little power, as the recent energy bills have been quite high. The problem is, I don't think the 7770 has enough oomph for what I want. Is there a middle of the road card that has more gaming power but doesn't suck up the wattage? I was thinking something along the lines of a 560 Ti, but the power consumption is night and day in comparison.

Thanks in advance.