Need help choosing mobo,ram,psu

RAM: G.Skill PI Black DDR2-800.
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231209

MB/PSU: GA-EP45-UD3P and Corsair 750TX if you want the option to add a second video card later. GA-EP45-UD3R and Corsair 650TX if you are sure one card is enough.

It really depends on your monitor. For 1680x1050 or less one HD 4890 is plenty, IMO. For 1920x1080 or more you should keep the Crossfire option.

If u open to AMD options

Non multi GPU
Gigabyte AM3 770-UD3P
P2X3 720BE
2 X 2 Gskill DDR3 1333
GTX 275

Multi GPU
Biostar AM3 TA790GX A3+
P2X3 720BE
2 X 2 Gskill DDR3 1333
HD4890

^
I'd look at the AM3 boards as well, it gives you more of an upgrade path as opposed to the LGA775 intel chips. The AMD Phenom II's are a great value and perform extremely well.

Good choice on the 4890. They are AWESOME cards.

Are you going to be overclocking your system?

Thanks for your advices  

Yeah, I am gonna OC to the 3.6ghz mark. Is the gskill ram good for cpu overcloking because I know not all rams can work well if the cpu is OC'd.

OK, if you're going with the X3 720BE and the TA790GX A3+ then you need DDR3.
http://www.newegg.com/Product/Product.aspx?Item=N82E16813138141

I'd buy this one:

G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 $60
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231189