If you are searching around on the internet for free MP3's by Dr John MacArthur, you'll discover what's commonly called "not muzzling the ox while he's treading out the grain", ie. you'll have to purchase most of John MacArthur's sermon (apart from a few on Sermon Audio and about 40 on Sermon Index), which is still absolutely worth doing, and has enabled the CD/Tape/DVD distribution ministry of sermon's by "Grace to You", to continue for nearly 40 years! (As well as books, articles, and other literature).
BUT!!! As of Wednesday the 5th November 2008 "Grace to You" - the ministry of Grace Community Church, Sun Valley, California, will be "opening up the vault" to enable FREE access to 3500 sermons (no registration or anything else required). Simply go to http://www.gty.org/ starting this Wednesday!!! Thankyou Grace to You!