I've looked at a bunch, and tried a few.   Below are three.  I'll keep reading and experimenting.  Soon I'll have this site set up so that you can write your own reviews in the forums section and rate the products you've tried.

 First, there's the one I purchased, the Self Hypnosis and Relaxation Machine (SHARM).  SHARM lets you build your own multi-track meditation audio sessions using three different methods, binaural beats, monaural beats, and isochronic tones.  See the SHARM Overview for a complete description.

Here's the shareware BrainWave Generator.  You can use it free for one month, then registration is $40.  It's free to try so see if you like it!  http://www.bwgen.com/download.htm  I haven't played with it much but it looks intriguing

Of course I looked at and tried the HoloSync sample from Centerpointe.  I say "of course" because this is probably the most well marketed product.  See: HoloSync   My only wish is that their sample would be longer on the meditation with a bit less talk.  IE. it would be nice to really try out the meditation, then hear the marketing pitch.  On the positive side, I heard about this product from a friend who's really into meditation, says it's really good and has achieved great results.  Check it out.  If you want a good, ready-made meditation system, this is top-rated.

  How could I not try the free one, SBaGen?  Easy.  It's not so easy to find.  This one is very nice because it let's you create your own binaural sound tracks, and then you can mix them with any foreground sounds you would like.    It's pretty easy to use on Windows, IF you read the documentation.  There's no GUI.  It's open source and you are required to give away any tracks you create that use the supplied foreground sounds.