Blog Ads — Which Ones Are the Best?

It is not a huge issue whether I make money or not through my blog, but I would like some advice so that I have a better chance at making some revenue.

I know there are a lot of sites out there that offer pay-per-click or other ways of making money.

What ones are the best?
Do you have any suggestions for making the most use of the ads?

PS. I do not want to annoy people, so the less obtrusive, the better. Thank You.