There are many companies that will pay you to post an ad or a review of a service, product or website.
I recently complied a list of sites that I know of that pay bloggers. You can find that list here:
Want to make money blogging?

My favorite out of them all is Pay Per Post. This site seems to have the most opportunities available (most of the time) even for those who have a 0 page rank. Unfortunately, my blogs (I have 3 approved with them) are a page rank of 0. At one time this blog was at a page rank of 1 and it was amazing how many more opportunities I had to choose from!
I have also realized having your own domain name is much better. There are more opportunities available to those with a unique domain name. My other 2 blogs are Blogspot blogs though~

I was recently asked how much money I make in a month doing this and really, there is no set amount. It's all luck, for the most part. Just like last night, there was that $500 opportunity available. I never got a chance to do it, the opportunities were snatched up so quickly by other bloggers. I did manage to do one for $8.50 but that was all I could get yesterday.
Some days I luck out and am able to do 3 or 4 posts. Even at $5 a post, that's still $15-$20 a day, which is over $400 a month, but that doesn't happen every day.
One day I was able to do 2 posts. One paid $15 and the other paid $35. That was a quick $50.

I have a run down of how I have been doing HERE

If anyone has any questions, please, contact me at:

unbalancedlibra@ymail.com