vActionbar from curse.com Caution: Iffn yer done doth be prone ter crashin alot, it might no set up properly, an yer twill haver ta swap classes after crashin ter reset it.
The addon that Lemon suggested is probably the best 1. Personally using Extended Action bars and anything else that adds more bars drops my frame rate too much. Once you have your action bars set up on a class combo type in '/abar save' to save the bars how they are. You can then switch and do the same with all your other combo's. Once that's done restart the client to make sure your settings save.
With what Lemon said about swaping classes to reload a setting, you can also type '/abar load' to restore the bars to what ever you had saved last.
http://rom.curseforge.com/addons/vactionbar/