I always thought that the way that Lyn had his shaman shields set up was rather nice. Water/lightning shown to the right of the player frame, earth shown to the left of the target. Having the charge number to the right of your player frame and moving the cast icon to the left would seem to look alright. I mean, you should know what you're casting so it doesn't really need to be more towards the middle of your screen (although I haven't seen what it looks like in action).
http://s.wowinterface.com/preview/pvw17962.jpg
Edit: Photoshoped this up real quick to see how it might look assuming that your player and target castbars are relatively similar.
