Kroeran, I was also interested in some actual feedback from meditation to see if I was getting into the right brain states. I got interested in this after watching a YouTube video of David Lynch talking about TM. In the video they have a student who has been practicing TM come up on stage and they hook him up to a machine which is displying brain activity on a big screen so that everyone can see the proof of the effects that meditation has on his brain waves.
I do not know very much about measuring body states. Just from poking around on the net, it looks like maybe an EEG machine is what you need to see the brain waves. Here is a Wikipedia entry on this. They even talk about which frequencies relate to which state - alpha, beta, zeta, etc.http://en.wikipedia.org/wiki/Electroenc ... e_patterns
Unfortunately, I could not find one that was very cheap although I did see a couple of discussion groups that were talking about how to build your own for $100 or something. A couple grand seemed too high a price for me to pay since I think that once I saw proof that I was getting into the expected brain states, I would not need to see that ever again. Of course it may be very interesting to see if the brain waves change when having interesting experiences (OOBE, etc).
I would be interested to know if other members are using any sort of feedback devices like this and if they think they are useful for entraining.