I thought the Secret Agendas rules and cards from Town Cryer 18 were interesting, but rough around the edges so I decided to make my own deck using Twan van Laarhoven's Magic Set Editor. It can be downloaded at http://magicseteditor.sourceforge.net
I haven't modified the scenario rules at all, but may at a later date. If you want to use my deck or see an example of a deck, you can view the pdf here (4MB). The deck file for the magic set editor can be found here. I printed out the deck on heavy cardstock paper, cut them out and put them in card sleeves for use whenever my group plays multiplayer games. We'll be using them in our campaign starting tomorrow night.
If you come up with your own deck or ideas for Secret Agendas or some other cool multiplayer variant/scenario please post them!