I've been pondering much the same.
I've been eyeing up this
Slik AF2100 Trigger Tripod Head for my existing tripod as at the moment I use a pan and tilt fluid head which is great for macro and portraits etc but really frustrating with a big zoom and a moving target.
Anyone got any thoughts on this or could say whether it's a good suggestion.
I also know someone who uses a gimbal style head which he swears by, but they're a bit out of my price range. To the OP: I suggest you state a budget as you can spend quite a bit on a tripod and head.