Songs or riffs I have figured out how to play on the guitar:

Danny Boy (surprisingly easy)
part of the A-Team theme
Play That Funky Music
Day Tripper
one of the Looney Toons themes
Do You Feel Like I Do
Sunshine of Your Love
Something
There's a Place
Sunshine, Lollipops and Rainbows (suggested by my mom as an example of the first 2 notes going down a major sixth)
My Bonnie (up a major sixth)
Here Comes the Bride
The Futurama theme
The Star-Spangled Banner
The Daily Show intro
O Come All Ye Faithful (since it's first few notes are the same as Colbert)
The Colbert Report intro
The original Battlestar Galactica theme
The First Noel
What Is Life
part of the Star Wars main theme
part of the Darth Vader theme
Frere Jacques (which was also my first piano song)
that bit from Close Encounters of the Third Kind
Smoke on the Water (of course)