A list of probably obvious things to try:

HackerNews Delicious Links StumbleUpon Niche blogs - There are people who don't get a lot of freebies who will actually do a full write-up in exchange for a free trial etc. Without knowing what your product is, it's hard to reccomend anything to specific in this category. Twitter - Tweet about new features, promotions, related news at least once a day. This is also a nice informal way for your users to speak directly to you in a public forum. Company blog - Get a Tumblr or something and have this feed to your tweets as well. Facebook page

Out of curiosity, what's the audience?