Every popular blog (and the giant Google too) come up with something weird, new, controversial or funny every year on April 1st. Yes, April Fool’s day is the one when you can do just anything weird with your blog or your readers. The more weird and close to reality your prank is the more buzz you will get. If you had not tried it yet, be sure to pull a Prank on the next 1st April. So these were the ‘Out of the Box‘ methods that people (Marketers to be more precise) are using around the web.
+1 point to adsense. I guess though that the OP doesn't like adsense for some reason or it doesn't fit his site. The next in line has to be CPA networks of course! And buysellads is a very good option tbh.