A few days before the election a senior staffer of Obama's revealed that Obama was big collector of Spider-Man and Conan the Barbarian comic books. When Marvel Comics learned of this they decided to included Obama in a Spider-Man comic, and published the story "Spidey Meets the President!", written by Mark Waid, in The Amazing Spider-Man No. 583 released January 2009. The issue proved extremely popular and sold out in a matter of minutes, and copies could be found on eBay going for $300 less than a day later.
Mitt Romney hasn't appeared in any comics that I've been able to find outside of what I've already reported except for several appearances in Doonesbury, most notably with a story about Romney's time in France, which you can start reading here.
On the web, numerous webcomics have featured Obama, most notably Sinfest (above) where Obama is depicted as a hip man with quasi-mystical powers. Other webcomics that have had political and social jokes referencing the election include Diesel Sweeties (right), The Non-Adventures of Wonderella (below left) and Saturday Morning Breakfast Cereal (below right).