We've decided to encoroporate not just digital textures but painted, hand crafted textures too for our city which will be made in Maya. As these textures will be UV unwrapped I've decided to make them as simple as possible so that I can join them together pretty much seamless.
I've begun one which revolves around paint. I let the paint dribble down the card, and added in more colours and white to mix it all up. So far I'm quite pleased with what's come out.
(excuse the horrible quality, I'm having to use my webcam as my camera whilst I don't have my Nikon available)