If you’ve gone with a self-hosted WordPress site like I suggested, you’ll have literally thousands of amazing free and paid theme options at your disposal. Plus, once you buy a theme (which are relatively inexpensive investments) like the one I use for my blog here, OptimizePress, you'll own it forever and get all the benefits of excellent support and customization options that come with premium WordPress themes.
Perhaps the most popular network for placing these types of ads is Google AdSense. With this program, you do not need to be in direct contact with advertisers; you simply place the banner on your site, Google chooses ads relevant to your content, and your viewers click on the ads. There are countless similar programs available if you find that AdSense doesn’t work for you, such as Chitika, Infolinks, and Media.net.