Have a look at Kingston and some of their resellers. I got a good deal on Apple-specified RAM 512MB for an iBook from ebuyer £46 rather than the £72 that Crucial wanted tho Crucial were cheaper for a GB.
I'd cut and paste the Crucial part number for your Mac and the Kingston memory number for your Mac and then go to Kelkoo or Dealtime and run a search on it to find out which store is cheapest.