Noiz2
Sound Ninja
Have you thought about something like V-Control Pro for iPad?
Just personal taste but I cant stand mixing with a non tactual surface. You have to take your eyes off the picture to find the fader, no feed back and you could have slid off the "fader" on to another "controller" while "mixing". To me this is a bit like the non motorized control surfaces where you have to "catch" the controller.
Someone who grew up on virtual devices might feel differently, but I hate them.