Hey SGP,
The most reliable power supply manufacturers are Corsair, Antec, Seasonic, and OCZ.
I would suggest this as an inexpensive option:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817341016&cm_re=ocz_psu-_-17-341-016-_-Product
Are you committed to a GTS 250? If you want advice on this choice we would be glad to help here as well if you post your monitor info and what kind of games, etc you want it for.
This is a pretty good deal:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814261057&cm_re=gts_250-_-14-261-057-_-Product