Don't forget that the MCAT is changing slightly for 2003--more molecular bio and biochem replacing some of the o-chem, or so I've heard.
My top picks are:
-PHYSIOLOGY (animal/mammalian)
-Biochemistry
-Genetics
-Cell Bio
-Micro
-Molecular Bio (although my experience was that genetics, cell bio and biochem cover most of the topics that molecular should anyway)
-Literature courses if you haven't read anything except for science textbooks for the past couple of years for practice for the verbal section
-An essay writing course (read: creative writing, etc.) to help prep for the writing section...hey, it can't hurt.
Don't bother with anatomy, histology, or neuro for the MCAT, but I hear it helps just a little bit for the first year of med school.
Good luck!
P.S. Don't think you have to take all of these courses before MCAT time. Physiology is most definitely key, and then take at least one or two of the following: cell bio, genetics, biochem, molecular. More is okay, less could be fatal (or at least really bad). Also, consider that a lot of medical schools are now requiring either biochem, molecular, and/or genetics. Double check the schools you are interested in to make sure to take the needed classes before you graduate.