I always use crucial.com as a barometer and it's usually harder to get better prices in the UK. Checking US prices I see it is a little cheaper than the UK currently, (but I'm guessing that's without sales tax whereas ours includes VAT), but not significantly cheaper.
So tempting to get 4GB at the moment as it's just dropped by almost £20 in the UK. Not sure I need it. I run the internet just fine on 640MB and Panther on a 12" PowerBook G4, and don't seem to be running high end apps too often on my MBP or iMac at the moment. If it dropped below £40 though, I'd eat it up.