Well it doesn't depend on the brand of the card only a personal pereferance. The E521 uses a 305W Dell PSU with 18A on the single 12V rail (I think), its a BTX case but people have succesfully modded it for a standard ATX PSU like Corsair. Also for the 8600GT I personally suggest XFX or EVGA.
Thing is......for a brand like eVGA theres only one online and thats at NCIXUS.com and it costs around 130.00+ but you can purchase a 9600GT from Newegg for 100.00+ and it is even the EVGA SSC Edition.
EVGA SSC 9600GThttp://www.newegg.com/Product/Product.aspx?Item=N82E16814130445
EVGA 8600GT http://www.ncixus.com/products/26888/256-P2-N768-A1/eVGA/