Savysugar.com had a pretty cool article on "uncycled" gift wrap ideas: http://www.savvysugar.com/DIY-Upcycled-Gift-Wrap-26089441 
I'd never thought to use some of these things as wrapping paper before, but I'm going to look and see what we have. They suggested things like maps, sheet music, posters, pages from books, pretty paper shopping bags, etc.
I'm pretty excited to see what I can come up with! What are some things you've repurposed for wrapping paper?