Adobe® Media Player
http://labs.adobe.com/technologies/mediaplayer/
Back in 2006 MAX conference, someone asked whether Adobe would release a FLV Player. They replied that they had some plan. 2 years later, their plan was finally revealed. More than just a FLV Player, it’s also a desktop YouTube and it is “professionally very very pretty”.
Coming out at the same time as AIR, it’s a perfect “one stone two birds” strategy. If you want to try AIR you definitely should start with Media Player because it’s by far the most useful AIR application for everyone (not only for developers or designers). If you want to try Media Player you have to install AIR.