I have used three, lPanel, CE and AutoPilot. AutoPilot is probably the most advanced overall of the three, but for me was a bit of work to setup. Very different.

I forget, I used phpCoin a bit to. Nice as it is free, but the admin area is rough. I understand from the last time I was at their forums they will be producing a pro version. Not sure what that means for the free version.

In general, ClientExec is the one to use.