Yes, you can display ads other than AdSense. There are so many types of ads that’s it’s really a tough question to answer.
Also, depending on your niche, you have to decide whether you want text ads, image ads, or both. Then you’ll need to find ads that you’d like, usually either directly with the company or through an affiliate network.
Regardless, they’re pretty much done the same way as AdSense if you’ve done that already. Typically, you just have to add a snipet of code to a text widget or within the body of a post.
Sure you can use Adsense ads with other type of ads in your blog. But they have some TOS on this. You can’t keep Adsense and other contextual ads very closely in a way that its difficult to differentiate.