I have been using Hemi-Sync for about 3 years now and have seen tremendous results. I highly reccomend the Gateway Experience as a portal to self discovery. If you have ever experienced a seizure or epilepsy, or have any other ailments that affect the brain, you may want to consult with your doctor before using any kind of assisted brain entrainment.
To help increase focus and concentration withought using outside technology for brain entrainment, try focusing on the breath. Breath in for a count of six, hold it for a count of two, breath out for a count of 6, pause for a count of one, then repeat. There are countless exercises that help improve focus and concentration; i prefer those that deal with the breath because allowing natural, unrestricted breathing leads to relaxation.
If you would like to try a free sample of Hemi-Sync, J.S. Epperson has a Myspace page with a few of his songs that you can listen to
here.
There is also a free manual available on the subject of focus and concentration called, "Ther Power of Concentration," available
here.