Amazon's Relaxation and Meditation category is a good source of tapes/CDs, though the emphasis is on self-help (also note the delivery charges). Amazon.com.

The Sheffield Yoga for ME/CFS website has good reviews of both relaxation and yoga tapes/CDs.

Relax UK has a good selection of guided relaxation and relaxation soundtrack CDs.

Eli Bay's relaxation tapes and CDs This Canadian site is unique in having good descriptions of all its relaxations. So, no need for me to give full reviews, but I have tried and really like: Autogenic Relaxation, The Healing Light, Focused Relaxation (review), Cortical Relaxation and Expanding focus. Tapes are the same both sides, while CDs are have two different relaxations. Very reasonably priced, and available worldwide from The Relaxation Response Institute

Diana Lampen has a good selection of her own relaxation and yoga tapes for £6 each (CDs £8), both inc. p&p worldwide.

Local Libraries may have relaxation tapes to borrow. And an increasing number of Doctors' Surgeries have tapes that they will lend to patients with stress-related illnesses.