iMac Memory Question

I know, I know, another question. But hey, I like to learn things and I want to be sure before I make the switch.

I plan to get the new line of iMacs, I'm gussing they will use the same memory anyway. But, where can I buy Mac memory from in the UK and what type is it? iMacs only come with 1Gb of memory and I have 2Gb right now in my PC, so I want the same amount for my Mac.

Thanks.