purging papers

This afternoon my friend Jamie came over to help me organize my office and hang up some artwork. We spent two hours categorizing a large box of papers and other mementos. For most of the items in the box I was able to find a home, but I still need to come up with an easy and effective way to file important documents, papers and newspaper/magazine articles.
How do you organize your paperwork? Do you use a large filing cabinet, a portable filing box or a multipocket expanding file? Do you keep all of your receipts or just those for large purchases? Please share your organization secrets! I’m desperately trying to get (and stay) organized.
(image source)