Handbills are a little more personal than posters since they're designed to be handed to someone. We've used them effectively to advertise events as well as campaigns.

One very effective handbill (sadly now lost) was a postcard pre-addressed to the university president which explained the argument against dissection the back along with room for a signature. Despite being too poor to provide stamps we were pleasantly surprised at how many people mailed them in.

Another important class of handouts are those picked up by people who come to your public tablings or meetings looking for information. These are crucial. These people are your primary target audience and the documents you pick up may be your only chance to communicate with them. You may want to try to order PETA handouts for this purpose, as we did.