The Kaplan book is pretty good, but even better is the practice tests that AAMC sells. These are actual previous exams. They are a bit expensive (check here on the For Sale forums or on e-bay or other auction places for used ones) but you can't pass up on having real exams to study from. They are available at
http://www.aamc.org/mcat
The next best book (in my opinion) is the Princeton book. Stay away from the ARCO or REA books...they have good information if you are having trouble with the material but their practice tests are awful. Peterson's isn't bad. I haven't looked at Lippincot.
For extra practice with reading comprehension, use any professional/graduate school admission test's study guide. Practically every type of graduate school has an admissions test and the Reading Comprehension sections are very similar between them. You must be able to read and comprehend quite quickly on the MCAT. There is a lot a material and not a whole lot of time.
As far as the MCAT essays, all the possible choices for essay subjects are available in the 2001 MCAT announcement available online at
http://www.aamc.org/mcat or check with the testing office at your university. They will choose two of these possible questions to present on the MCAT. I suppose if you really wanted to prepare you can write a full essay for each one before testday, memorize it, and repeat it on the test...but that's impossible so you can't.
Have fun studying. Cheers.
[This message has been edited by mpp (edited 02-26-2001).]