Besides weathering a prop, it would seem that documents is the next prop that low budget filmmakers overlook. They could be anything from a top secret government file or papers from a insane asylum or just a yard sale flyer. When propping up a document it's important to make it as believable as possible.
Keeping that in mind, Propnomicon, which is quickly becoming the go-to place for believable props, mentioned this link which is a company, aptly named Prop Docs, in which all they do is make documents of any quality and number and from anywhere your heart's desire. The best part of it all is that they include samples of their work. Keep in mind not to directly rip off their files for your next flick, but to help you get a an idea as to how your next document prop should look like. Go here for more details.
Also if you are searching for document props that are a bit more vintage check out this link, which although is not for commercial use, you should be inspired enough to create your own original documents.