If you have an Apple Mac and have been thinking of upgrading the memory in it, it pays to shop around, as there is a huge difference in prices to be found.
When I bought my Mac Pro I wanted to stick 4GB of memory in it, but due to the machine requiring a specific new memory type, there were few suppliers and so prices were ridiculous. Around October 2006, Apple wanted around 1600 euros for 4GB RAM which I considered unacceptable.
Even today, in October 2007, Apple seems to want around 230 euros per GB of RAM for this machine!
I just bought 4GB RAM from OWC and it cost me around 40 euros per GB including carriage from the USA and only took 3 days to arrive! This RAM has good feedback from users on the web so I had confidence in its quality. I have run Rember on the RAM and it has tested the RAM and passed with 100% success. There are many other suppliers like TransIntl, Crucial, Kingston etc that may be worth considering too. Check user feedback in forums to be sure that people have not experienced problems with the memory you are considering buying.