I mentioned Valkyrie Sky earlier — it’s a “freemium” MMORPG from Korea (freemium MMORPGs seem to be a major export for that country). I’ve also been seeing Flash games on Kongregate run this model, apparently since Flash developers also want to eat as well.
For those not familiar with the free-to-play model: you can play it for free, but if you want to look cool it will cost you. Purchase better equipment and items, skip all of that boring grind. It works particularly well by feeding on your psychological weaknesses — by the time you’re looking at the real-money-for-fake-item shop, you’ve already invested 10+ hours into your character. It’s escalating commitment against sunk costs.
Granted, Valkyrie Sky has a lot more skill involved in the gameplay than World of Warcraft‘s “spam all of your abilities” battles; you can grind bosses down with your wimpy attacks, as long as you can do it within the ~10 minute time span without getting hit. I don’t think I’ll be buffing myself to redonkulous DPS just yet; I’d be missing the challenge.