Here's the scenario - your MMO isn't really gaining players, and your current players either don't like the idea of a subscription or you've created too large of a gap between players who pay for perks and those who don't. What's a producer to do?
Well, you probably haven't considered effectively using your existing playerbase to market your game for you. Consider taking your most die-hard players and incentivizing them with free play time or in-game currency to act as an online 'street team' for your product. There's no better advertisement than happy players who gush about your product.
The easiest method involves submitting some weekly news content to major social networking sites; you can then build a tracker and reward players who 'like' or 'digg' your content, thus increasing your ranking/popularity on said websites. The content of your articles should be relevant to your product, but also relevant to other similar products in your market (RPG games, role playing, text games, hack n slash, etc).