Get the 7900GT. It always wins in benchmarks against the X1900GT, and is an amazing overclocker.
Get the eVGA GeForce 7900GT KO Superclocked version from Newegg. At $290, its $20 more than the base 7900GT, I think.
Other good brands include BFG, XFX, MSI, and Leadtek. eVGA is the best of them all though.