If you are going to get a 550Ti, get a 7770. Its faster and usually about the same price.
The 7770 is a really really good card, whereas the 550Ti is older and uses alot more power. Its also slower and overpriced. http://www.newegg.com/Product/Product.aspx?Item=N82E16814127687
This one is $110 with rebate, and $125 without.