The Adobe Platform Docs team has released a beta version of the new combined version of the ActionScript Language Reference called the Adobe ActionScript 3.0 Reference for the Flash Platform.
This reference documents the ActionScript packages and classes from Flash CS4, Flex 4 (Gumbo), Flash Player 10, AIR 1.5, ColdFusion 9, and LiveCycle Data Services 3. So if you use more than one of these products you no longer have to jump around from reference to reference. You can find it all in one place.
There is also some nifty filtering logic in place so you can hide content from products or runtimes you're not interested in. You can even step down to previous product versions.
This is still in beta, and there is a feedback link on the site, so please have a look and let the team know what you think.
Here's the official announcement from the Platform Docs blog too.