Just like link swapping, some companies have banner swapping programs. Most banner swapping programs are free and some might require you to pay a monthly administration fee so they can cover their costs.
Many of the free companies make money by the in-proportionate ratio of banners you display on your site, vs. your banners being displayed on other sites.

This is how they make a profit. Their arrangement yields them more banner ad spaces than actual banner ads they need to place for their members, so they can sell the extra banner ad spaces to paying advertisers.

The advantage of joining a banner exchange program is it's a free way to get other sites to post your banner ads. The disadvantage is that you give up a lot of control over where your ads are posted and what ads are posted on your site. In most cases, the banner exchange program chooses where to put its members' banner ads, and you may not like what they decide to post on your site or where they end up posting your banner ad. Most banner exchange programs attempt to link banner ads and sites intelligently, and they often do a good job, but there is a possibility that at some point you will be dissatisfied with a banner ad that ends up on your site.

At the end, I would just like to say that the deal is yours. It is worth searching around and doing good shopping if you can find banner exchange programs to your liking. You might want to keep a contract so that if you don’t like what is being pasted on your site, you know it won’t remain there for long.