Which 512mb ram to add onto mine?

[Vegeta]

Hi I want to add 512mb ram onto my current Geil Ultra cas2 512mb ram, I do have 1 gig of ram however the 2X256mb Geil Ultra cas2 ram have trouble all being used in all three slots - im guessing i need 2x512 dimms.
I cant find another Geil Ultra cas2 512mb ram ANYWHERE! so what should i get? I dont overclock the ram at all i run it so that my barton 2500+ can run at 3200+.

 

[Vegeta]

Think i might go for the corsair then mate, I contacted ocuk but they said they've not had stock on that ram for months so im not holding my breath.