I've been keeping an eye on the 'population' of the WC3 server quite a bit since it's been moved, and it hasn't really been going anywhere (Unless you count the bots...)
One thing that could be done, however minor, is using some form of sig banner on other forums that you're on (If allowed there) like this:
You can even pick your colors by getting them here (for WC3):
GameTracker.com : (css) Counter Strike Source Server Banners
For any of the other servers, just click on the banners under the server stats and follow the image/html banners links on Game-Tracker to get the appropriate code.