The GTX 550 Ti is alright but it is a last gen card. For the same price you can now get a 7770 which has lower power consumption and is plain better. It also OCs slightly to give another performance boost.
560's have been seen in the wild for ~$125 and are much stronger than a 550ti.
What's your price range?
Again, those cards are last generation. Although they're great, you can get better price/performance with this generation's cards like the similarily priced 7770 or 7850. And of course much lower power consumption.