How can I block ads for free in IE10 (both modern UI and desktop)?

Unfortunately nothing like this exists, but you can try to block ads the old fashioned way, with a HOST file. This is a special file that will block all traffic from domains that are suspected as being advertizements. Detailed instructions on how to use the file can be found here. Among my favorite block lists can be found here.

If you set it up in a special way, Internet Explorer's built-in Tracking Protection feature blocks ads -- and works even better than the HOSTS-file solution suggested in the answer Mikhail wrote.

IE has a built in ad blocker, you merely have to tell it which sites/adverts/cookies etc to block. Fortunately these lists have already been made. Just browse to http://www.iegallery.com/en-us/trackingprotectionlists and click add list and explorer will add it to the integrated ad blocker.

BTW, uses the same blocking lists (Easy-List) as ad-blocker on chrome