If you've created a site that's dedicated to a particular topic, one of the best ways to promote it is to jump in and join the community surrounding that topic. For example, if you create a web page dedicated to your favorite musical group, you might want to look into seeing whether there are online discussion boards or mailing lists devoted to that group. Not only might participating in those forums be enjoyable, but it also gives you an opportunity to promote your site.
Bear in mind, though, that most web users are quite jaded when it comes to naked selfpromotion. Joining a popular Rolling Stones mailing list and immediately sending a message telling everyone to check out your site will only put people off. Instead, join up, follow the course of the discussion, and chime in when you have something interesting to add. If there's a page on your site that's relevant to the discussion, post a link to it.
Such participation is the very essence of becoming a full-fledged citizen of the web community. Nothing will increase the popularity of your site faster than becoming a respected member of communities related to your site. Even big companies have figured this outrather than avoiding online forums where their products are discussed, many are now assigning employees to participate in those forums. The marketing jargon for this sort of thing is evangelism, and some companies have honed it to a science.