If you own one of the new unibody/Late 2008 MacBook Pros or one released November 2007 or later you can use up to 6GB of RAM – the most on a portable Mac.
The new MacBook Pros have two slots and the 2GB model ship with a 1GB SO-DIMM in each. The 6GB upgrade requires replacing the two 1GB modules with one 4GB SO-DIMM (the expensive one) and one 2GB module (~$30). Keep in mind that the unibody MBPs require DDR3 "PC3-8500" SO-DIMMs running at 1066MHz.
I did a little shopping for a 6GB kit (1x4GB, 1x2GB) and found the following prices:
- TransIntl - 6GB kit – $378
- OWC - 4GB ($360), 2GB ($35), total $395
- Crucial - 4GB ($390), 2GB ($36), total $426
- RAMJet - 4GB ($400), 2GB ($35), total $435
I ended up getting my memory from OWC.