If you don’t mind Japanese text, you can play Patapon 3 right now. A downloadable demo is available on the game’s Japanese site. Here’s a direct link to it.
Click on the download button (the icon on top), save the zip file to your hard drive, and copy the contents to “PSP\GAME\NPJG90088”. Takes about five minutes to setup per PSP. You’ll want to give this file to your friends too since the demo supports ad-hoc multiplayer.