Affiliate Marketing Secrets

I’m developing a niche site that should have lots of repeat visitors. (They create a free account.)
The target subscribers will be very scattered around the world but united by acommon interest.
What’s the best way to sell adspace?

I’m in the process of building a unique website that should attract a good number of repeat visitors in a niche market. I personally think most ads are sooo annoying. But then I want to make money too.
The website will offer an ongoing service and develop a semiloyal following who will hopefully refer their friends. So I could charge for subscriptions or sell adspace or both.
For simplicity sake it seems the best bet would be subscriptions, but then I would lose so many people who are looking for a freebie. I would retain some paying customers though.
I wouldn’t know where to begin by making money with ads, but then everybody would run to my site because it was free. What do you guys think? Should I offer free accounts with ads and paid accounts without ads?