Do you also have a pile of unused domains, collecting dust and never got the chance to hit cyberspace? Have you heard of Google AdSense, who provides you with a way to monetize on online ads?
Anyway in case you didn’t know, Google AdSense have for some time supported AdSense for your “parked” (unused) domains, the only thing you need, is the ability to manage the DNS of your parked/unused domains.

First of all you will need a Google account, if you don’t have one yet – start by creating one right now! When you have your Google account ready, then you need to create a Google AdSense account.
After signing up and logging in to Google AdSense, then navigate to “AdSense for domains”, here you will be able to add all the domains you want to associate with AdSense.
Add the domain(s) you want to associate, then confirm. After the confirmation you will get an receipt displaying 4 different IP addresses, you will later need these to setup the proper DNS A records for the domain(s), you also get 1 unique Google URL, representing your personal pub-id, this will later be used as the DNS CNAME for your domain(s). Thats it for the AdSense part!

Now you just need to change the DNS settings for your domain(s). To do that, you will need to do the following:
First you need to setup 4 A records, using the 4 IP addresses provided by Google, you will end up with something like this:

And finally you need to setup a CNAME for the domain, ending up with something like this:

Note: It can take up to 24 hours before the DNS settings for your domain(s) get updated!

Thats it! Now when you login to Google AdSense, you can follow the stats and earnings of your domains.
If you want, you can optimize the ads displayed on the page(s) of your parked domain(s), by associating specific keyword(s)  to the domain e.g. relating the context of the domain-name.