SEO is the key. Takes a ton of time (and time is definitely money), and highly competitive in the online gambling space, but once you have it right, the traffic flows in for free.
If your site is new, which it sounds like it is, you can do well in MSN and Yahoo in a relatively short amount of time, but it is widely believed that Google applies an aging filter (aka “sandbox”) of 6-8 months before they let you rank for your keywords. We launched in January and are still in the sandbox.
Check out seochat.com and their forums, tons of information to wade through.