An interesting variation on F2P is the one used by World Golf Tour [1], which I've been playing a bit recently.
Instead of forcing users to pay real money to get better equipment, it has another means of earning credits: viewing advertisements. That means that a) I don't feel like I'm actually spending money (except opportunity cost), and b) they can show pretty well-targeted ads to users who are requesting to see them. I don't know the financial details, but I'd guess they can sell for a pretty decent rate. And you have to view quite a lot of them to get as many credits as you could have bought outright for $10.
As an added bonus to them, relying on ads means I have to disable AdBlock for their entire website.
Instead of forcing users to pay real money to get better equipment, it has another means of earning credits: viewing advertisements. That means that a) I don't feel like I'm actually spending money (except opportunity cost), and b) they can show pretty well-targeted ads to users who are requesting to see them. I don't know the financial details, but I'd guess they can sell for a pretty decent rate. And you have to view quite a lot of them to get as many credits as you could have bought outright for $10.
As an added bonus to them, relying on ads means I have to disable AdBlock for their entire website.
[1]: http://wgt.com