Websites
Create a website for your radio program and dont skimp on the domain. If you do a radio show called Dark Tea Leaves then make sure you register DarkTeaLeaves.com (which by the way is open as of this writing.) Do you realize you can register your own domain for just a few dollars? Registrar companies like Omnis (Buy Direct) let you register your domain for as low as $7.95. Its worth a few dollars to have a real domain instead of a URL that looks like the opening sentence to a Charles Dickens novel.
Search Engines
This is a no-brainer. Visit as many search engines as you can and submit your URL to be spidered. For an easy starting point, go to Google.com and type in submit URL and watch all the results that pop up to get you started.
Newsletters
Start a newsletter about your radio show. If you have a website, put a link on it so visitors can sign up. Mention your newsletter (and website) at the end of your radio show. Bravenet offers a free newsletter service that's easy to use and creates html newsletters that good great.
More Cheap Tricks:
Give out business cards with your shows name, when and where it can be heard. VistaPrint (Buy Direct) offers free business cards for a slight shipping charge.
Visit websites which might complement your shows subject matter and try and arrange cross-promotion banner on their site for a short :15 commercial on your show.
Put a sign in the back of your car window with your shows name and website. (Make sure it doesnt block your vision.) Think of how many people each day will see it.
When promoting your radio show you can be as creative as you want and remember: a small budget should not stand in your way. Good luck and let me know how things turn out.

