This could include traditional ads to the side of the page content, ads that show up in the market feed, a special type of market that is an ad, etc.

Personally, I'd love to see a special type of advertising market that integrates with advertiser metrics and resolves automatically, and gets promoted on the homepage. Then advertisers could create a market like "Will at least 90% of people who buy our product mark that they were satisfied with it a month later", write up a blurb for their product in the description, and then the market resolves automatically somehow. This would allow people to advertise on Manifold and help subsidize the platform while still subscribing to the truthfinding ethos we have here.