Now that I'm considering using textures in my illustrations professionally, I'm being way more picky about my texture sources. I've come across so many free texture sources that are largely composed on textures made from copyrighted images OR just ripped off from other texture sources.
I've been a fan of CG Textures for a while, and decided to opt for a paid membership for more user-friendly interface, higher daily download quota and access to higher-res textures.
Anyway, I liked the texture above so much that I decided to just draw my Daily Doodle right on top of it. :-)