From what domains do app ads come from?

I have a rooted phone and block ads by adding domains to /system/etc/hosts. But so far I was unable to block ads in apps because I don't know what domains they are coming from. I tried to find this out by using OS Monitor but that only gives IP numbers and it looks like they all belong to google (no surprise there) but I guess google uses a couple of domain names for this.

So far I have these: tpc.googlesyndication.com, googleadservices.com, partner.googleadservices.com and a couple more which are not android specific for sure. What else are there?

I'm aware of various lists but they are huge and I prefer handpicking my own list.