The Flash Player beta is now available for various platforms including Linux. It is being made available for developers and consumers to test their content to ensure existing content plays back correctly and that there are no compatibility issues.

This beta includes 2 gzipped tarball packages for Linux: one is for the Mozilla/Firefox plugin and the other is for a GTK-based Standalone Flash Player. The plugin does not currently work in Opera browsers.

More info:
Beta Release Notes
Adobe Labs Downloads