Sonosync - Nicholas Webb. Relaxation through music that's in time with your resting heart beat. It comes as a triple CD, with three versions of the same album, each 'Sonosync' processed to a slightly different tempo. The music itself is very peaceful, and if I put one of these CDs on I'm usually deeply relaxed well before it ends. 
audio samples of all 3 versions.
Download £6.50+VAT, CD £11.95 from Shopsonic, plus shipping: approx 
£1.25; Europe £1.75; 
£2
Dawn Awakening has a good collection of music that isn't too New Age:
Free Spirit by Christopher Buckman; one of the tracks is called 'Floating on Air' that pretty well sums up the feeling of this album, which has lots of synthesisers and ethereal voices along with rain forest sounds. 40 minutes. You could also try anything by L'Esprit for music that has melodies, which are soothing without being sickly: his albums include Far Journey and Language of Touch. Midori's Spirit of the Pan Pipes is also worth a listen. Temple in the Mountain by Mark Hawkins is truly beautiful music in its own right - keyboards and synthesisers - that just happens to be relaxing, track Sense of Wonder (album only available by catalogue: email a request for one).
Tapes £6.95, CDs £11.95 plus delivery from Dawn Awakening , t 01803 864822. No audio clips as yet, but they will exchange any tapes you don't like. Delivery: £1 p&p per order £1 shipping for a single item, shipping at cost for multiple items - email for details.
SLEEP - various artists. A compilation of New Age music that sets out to send you to sleep has the potential to be mind-numbingly dull, but some of the tracks on this album are quite beautiful: I particularly liked Chant and Everlasting Road ( audio clips of all tracks). And, as the album has lulled me to sleep on more than one occasion, I guess it does do what it claims.
$10 plus shipping from Domo Records.
Calmtime - Graham Smith +. Music specifically designed to relax mother and baby. This CD uses humming, music and natural sounds to create a warm mellow lullaby-effect. Audio sample and more information from Calmtime.
£9.99 + £1.20 shipping worldwide.
iRelax downloads - Harry Henshaw These tracks combine relaxation music with binaural audio tones, which it's said can help move the brain into more relaxing and healing states. I found they make pleasant background music. The tracks, with titles such are Fantasia, Harmony and Serenity, are also available with a 'stormy night' or 'by the sea' background. Each track approx 15 minutes. Audio sample and more information from Enhanced Healing.
Mp3 downloads are $1.29 per track.
New World Music has a huge catalogue of relaxation music, with audio samples available for most CDs/tapes, t 01986 781 682. New World Music.
Sounds of nature
If you just want sounds of nature with no music, you could try:
- Relaxation-CDs.com have a series of CDs using sound tracks of the jungle, the ocean etc. Audio samples available for each CD. $19.95 inc. international shipping, with a 28-day money-back guarantee.
- Rainbow Falls DVD has and animated waterfall and river scene featuring the sounds of insects and birds and a flowing river during an English dawn chorus. Short video clip available. £8 inc. p&p from SSJ.
- Atmosphere is software (free lite version available) for creating sounds of nature soundscapes.