Most of the ones I had in 5.x still work great in 5.5.x, but I only use 3-4 actions per site. The ones that I do use are all core actions, so they got updates in 5.5.
I use the Scripties, PHP Feedback and a bunch of little ones for forms and things. Crowbar is another.
Walter updated Scriptys (see Actionsforge) and the others should be fine.
If in doubt try your pages in 5.5 before uploading - work on a copy document so that you have the earlier version to fall back on, but remember that FW automatically creates a version that you can revert to the first time you open an old version with the latest FW.