Submit your website to search engines and such. Word of mouth won't get you too far on the internet, even if your product is superior. You need traffic and hits. If you haven't already, you should submit your sites to google, yahoo, lycos etc etc. There are also other various website submittors out there, most of which cost money, but guarantee traffic and such. Craigslist is also a handy tool for free advertising/promotion.

With my business we have been using a lot of the free advertising as you suggested, but are now moving towards paying for banners/ads. Word of mouth has actually been pretty good to us as many customers have been referring their freinds, (one who actually bought a package for nearly every damn person they know), but it can only take you so far. I don't know many sportbetters, but I'll definitely keep your website in mind if the subject ever comes up!