On the admin side - new thread created.
On to the topic:
There are "brainwave entrainment" offerings. Basically, what these products do is present a tone in one ear and then a tone of a slightly different frequency in the other. So, for example, one tone might be 100 Hz and the other is 103 Hz. The result is that your brain "creates" a 3 Hz beat and then the brainwaves start to follow that beat.
Right now I'm listening to some of Jeffrey Thompson's stuff (the reference is
Center for Neuroacoustic Research) which is really neat because he takes these ideas and weaves them into natural sounds or electronic music. Kelly Howell's offerings are at
BrainSync.com and offers a different take on the same thing. And then annie just linked to another site above that I'll have to explore, but I don't know if they do theta.