Swipes I love, love, love my swipe file. A fat folder sitting on the corner of my desk, that baby contains all the direct mail I receive -- not just from nonprofits I belong to (or that are trying to woo me), but credit card offers, business-to-business mail, catalogs...if it comes to me through the mail, it goes into the file.
I mine that file for ideas nearly every time I start a new project. Many prove too expensive for nonprofits, especially those with small files. But often, even those expensive ideas can be adapted in some way for testing on smaller lists.
I cull old swipes once a month or so, but there are a few gems that stay in the file for several months.
Try keeping your own swipe file and see what new ideas you can put to the test in your mail program.