Altered states of consciousnes and shamanism are fascinating subjects.
I have studied and have experience with a wide variety of altered states and methods for inducing them, from psychedelics to meditation, drumming, strobe lights, flotation tanks, sweat lodges.
Of these, I found psychedelics to be by far the most powerful. Nothing else I've ever tried has come remotely close to being even a thousandth as powerful. Unfortunately, because of their legal status, I haven't done them for a very long time. I do think they have a lot of potential for constructive use, if done by a person educated in their effects and use, in a safe, supportive setting, with a knowledgeable, trusted guide, with honesty, respect, and a concrete, positive intention. In fact, here[1] is an interesting article about using psychedelics as an aid to Buddhist meditation.
As for shamanism, I've read The Way of the Shaman back in a university course I took on shamanism and witchcraft. Right now I'm making my way through Shamanic Voices by Joan Halifax (which I strongly recommend) and Singing to the Plants by Stephan V. Beyer, about ayahuasca shamanism in the Amazon.
Listening to 4 to 7 Hz drumming (per Harner's recommendation) has been a bit of a disappointment to me, although I haven't done all that much of it. Three or four sessions (at about an hour or two at a time) have resulted in either me falling asleep or some feelings of intense pleasure (much like I experienced in some deep states of meditation) -- but certainly no visions, much less "shamanic journeys". Overall, I think I'm more impressed by the effects of meditation so far. However, I intend to experiment more with drumming.
My one experience in a sweat lodge was literally torture. I'm not nearly masochistic enough to travel this path of inducing altered states of consciousness. There have got to be better ways.
My one flotation tank experience was interesting, and I would continue experimenting with it if it wasn't so expensive (about $40 a session). I'd liken the experience to something between meditation and dreaming or hypnagogic visions. Unfortunately, my consciousness was already slightly altered when I tried it, so I can't comment on how a "pure" flotation tank experience would be.
If I was ever fortunate enough to have another psychedelic experience, I would definitely like to try drumming, playing simple musical instruments, or singing -- as is done in many shamanic contexts. From what I've read, these may be effective ways of navigating the realms one is transported to.
Having the aid of an honest, experienced and knowledgeable shaman would also be very valuable. Unfortunately, I've heard that they are hard to come by these days, when Ayahuasca tourism and monetary considerations have enticed many less scrupulous individuals to pretend to be something they're not.
[1] - http://psychonautdocs.com/docs/stolaroff_buddhism.pdf