well i know OCZ is a good brand but look into G.SKILL. they are also a very good brand and are known for overclocking very well
heres a 2x 512mb
http://www.newegg.com/Product/Product.asp?Item=N82E16820231035
heres the 2x 1gb
http://www.newegg.com/Product/Product.asp?Item=N82E16820231034
heres a 2x 512mb
http://www.newegg.com/Product/Product.asp?Item=N82E16820231035
heres the 2x 1gb
http://www.newegg.com/Product/Product.asp?Item=N82E16820231034