Create a website from which to sell your beats. If you want to be consistent, then your clients need to know where to contact you when they need new beats. You can offer short snippets of samples on your website, along with an accounting of your experience and people with whom you've worked. You should also include your contact information, and -- if you wish -- your prices for beats.
Send prospecting letters or email to artists that may be in need of beats. While it's fine to send a prospecting letter to your favorite rapper or musician, chances are, he doesn't need new beats or won't be able to distinguish yours among the hundreds of letters he receives daily. Target up and coming artists that you see have potential and can make good use of a good beat.
Make mix tapes of your beats and distribute them. Even novice rappers that do it for fun enjoy listening to a good beat that they can rap over from their car or in the comfort of their own homes. Create a master mix of your beats and distribute them to family and friends. Once they begin playing it, you may then have someone professional ask who made it and where they can get a copy.
Make good use of social media sites. These sites -- including MySpace, Twitter and Facebook -- are all great for networking in terms of music showcases. Include clips of your beats on your pages and run frequent specials for new beats or to sell of existing ones to potential clients on your page.