Out of the easily accessible tests, Gold Standard and Berkeley Review offer the best practice tests. GS's FLs aren't as good as BR's FLs, but they provide a great bang for your buck. That said, recent test takers have said BR's tests are worth the extra cost because they're closer to the current MCAT.
Gold Standard:
http://www.mcat-prep.com/
BR:
http://www.berkeley-review.com/
For GS tests, check their ebay seller. They consistently have sales on their FLs where you can pick up all 10 for $100.