I would upgrade my current GPU. Atm I got a gts 250 1 GB.
I would buy a GPU that can run newest games at medium high settings at 1440x900 ( maybe 1650x1050 in future) for at least 3/4 year.
My budget is 300€ but I reach 400€ ( less I spend is better)
I'll buy the GPU on www.e-key.it
Got a 500 W PSU