How the ATB system and Stamina work in FFXIII was pretty good. Moves were assigned a certain slot cost so basic attack was 1 slot and more powerful attack's used more. As you levelled up you stamina bar grew allowing more slots for greater combinations of moves as you could stack them to release them in a combo. So if your stamina bar had 5 slot's you could launch 5 basic attack's in a combo. Or mix it up with 3 single slot moves and a more powerful double slot move. The system even had a built in auto attack that you could toggle on/off quickly. The whole system could be applied to FFXIV and each move assigned a certain slot cost and could probably do away with cast times to for mages just by increasing the slot cost for higher tier spells like Flare could use 8 slots or something.
Here is a video for anyone who hasn't seen it in action.
http://www.youtube.com/watch?v=S-pzptgE4a4
Ignore the Paradigm shift, stagger bar and all that nonsense, but how the actual stamina system itself works is great. When I played FFXIII and then started hearing the rumours of FFXIV and a stamina bar this is what I imagined it to be like on a next gen MMO. Infact I would even take the UI for the battle system in FFXIII over the current system in FFXIV. As a controller user, FFXIII seemed a lot more streamlined in the battle UI department.
*EDIT* Also spell animations like in the vid would be great too ^^