A therapy that slows brainwave activity, helping to produce low-frequency waves, is likely to aid relaxation and sleep. But it’s not only lowering brainwave frequency that binaural beats may offer to sleep and relaxation. A small study (19 people) has found that exposure to binaural beats is associated with changes to three hormones important to sleep and well being:

Tracks that move from alpha to theta can be a perfect vehicle for transitioning from a hectic day into a relaxing and rejuvenating sleep. Beginning with alpha waves takes you into a light but still alert meditative mind state where the difficulties of the day can be resolved and put to rest. Later, theta waves go deeper into the unconscious, preparing you for sleep and dreams.
Brain wave entrainment is a real phenomenon and is useful as one method of investigating how the brain works. But there is no evidence, nor any theoretical basis, for any long lasting effect on brain function or that there is any benefit of any kind. Despite this, there is a huge industry of devices that claim to train your brain waves and have a beneficial effect. I wouldn’t waste a dime on any such device.

The effects are strongest while you are listening to the tones because your brainwaves are synchronized and tuned into the frequency range you desire at that time.  After you've stopped listening the effects can still linger for a while afterwards.  The timescale will vary from person to person and be affected by what you do after you've stopped listening.

This is probably the most popular choice of frequency. The theta state is a state of tremendous stress relief. The benefits associated with theta level relaxation include improved concentration, reduced hyperactivity and improved memory. While in a state of theta relaxation, one’s blood pressure, breathing and heart rate all slow to a much more restful and healthy level that promotes natural healing. During theta relaxation one may also experience vivid flashes of mental imagery as the mind opens to memories or subconscious information that is not available to the conscious mind during the normal waking state. The theta state is a very deep state of relaxation that is excellent for deep hypnosis and mental programming.
Practice positive self-talk. It's easy to lose objectivity when you're stressed. One negative thought can lead to another, and soon you've created a mental avalanche. Be positive. Instead of thinking, "I am horrible with money, and I will never be able to control my finances," try this: "I made a mistake with my money, but I'm resilient. I'll get through it."
Many people experienced in using alpha brainwave entrainment report that the state of mind associated with alpha waves is a time when they feel most consciously connected to their subconscious mind. The intense experience of hypnagogic sleep, reported by some people as a feeling of being awake and asleep at the same time, is also associated with alpha brainwaves.
You listen to binaural beats using headphones. In each ear, you receive sound at a slightly different frequency (often accompanied by some relaxing background sounds). If your left ear receives a 300-hertz tone and your right ear receives a 280-hertz tone, your brain will process and absorb a 10-hertz tone. That’s a very low-frequency soundwave—one you can’t actually hear. But you don’t need to hear the sound for your brain to be affected by it.
Binaural beats, or binaural tones, are auditory processing artifacts (apparent sounds) resulting from the stimulation of the ears with two different sound frequencies. In fact, when two different vibrations are delivered to the brain separately through each ear, using stereo headphones, the two hemispheres of the brain function together to “hear” and perceive not the external sound signals, but a third phantom signal. This resulting signal, discovered in 1839 by Heinrich Wilhelm Dove, is called “binaural beat”. The effect on the brain waves depends on the difference of each tone. For example, if a sound frequency of 300 Hz is played in the left ear and 307 Hz in the right one, then the binaural beat would have a frequency of 7 Hz (“frequency following response”) which corresponds to the Alpha brain state, generally associated with relaxation, visualization and creativity. The beating tone is perceived as if the two tones mixed naturally, out of the brain. For the binaural beat effect to occur, the difference between the two frequencies must be small (less than or equal to 30 Hz), otherwise, the two tones will be heard separately, and no beat will be perceived.
Infra-Low brainwaves (also known as Slow Cortical Potentials), are thought to be the basic cortical rythms that underlie our higher brain functions. Very little is known about infra-low brainwaves. Their slow nature make them difficult to detect and accurately measure, so few studies have been done. They appear to take a major role in brain timing and network function. 
Alpha: Alpha brainwave patterns are associated with a state of wakeful relaxation. Slower and lower in frequency (between 9-14 hertz), alpha waves are dominant when we’re calm and relaxed, but still alert. Alpha waves are associated with states of meditation (your yoga class probably puts you in an alpha state), and also with our ability to be creative.
Sleep issues are becoming much more of a common problem. I think it's great to look at alternative ways to help with insomnia and other sleep related issues, especially when they don't involve the need to take medication. Something proved to be effective is 'Sleepstation' a UK based organisation who use CBT techniques to cure insomnia. Their online sleep therapy course is brilliant and very convenient as it's delivered online. Their website is definitely worth a look if you're having sleep issues

They are not beyond what is “normal” but for most of us they are outside of what is “typical”. Whether we consciously seek them or not, somewhere in the back of our minds we hold beliefs that because meditation and brainwave entrainment are beyond our usual set of experiences, then the evidence that they are having some sort of effect on us must also be outside of our normal range of experiences.
The functional role of neural oscillations is still not fully understood;[6] however they have been shown to correlate with emotional responses, motor control, and a number of cognitive functions including information transfer, perception, and memory.[7][8][9] Specifically, neural oscillations, in particular theta activity, are extensively linked to memory function, and coupling between theta and gamma activity is considered to be vital for memory functions, including episodic memory.[10][11][12]