Although even the largest site can include Google AdSense as an ad provider, if you're really looking to build a presence, you'll want to establish relationships with some of the other ad exchanges that can provide ads to your site. There are any number of providers you can reach out to.
For video ads, try these providers:
For display ads check out these providers:
There are plenty of others as well; a simple Google search for “online advertising network” will give you links to the many options you have. Some of these networks can provide you with display ads, others specialize in video ads, and some can provide both.
There are a few benefits of using a non-Google ad network to get ads onto your site, the biggest being that you're likely to get paid significantly higher rates. In addition, you'll have a better chance of speaking with a rep on the phone if you have questions or problems. On the flip side, many of these providers will require you to have and maintain a minimum amount of traffic, and they'll likely take a bit longer to pay you.