What lens have you got? I guess it's a tele zoom? If you have the 5D MkII you should really hold off until you can get yourself a REALLY solid ballhead. I have a 40D and a 100-400L lens and with a very big and heavy manfrotto ballhead I still have problems keeping it stable.
I'm saving up for a reallyrightstuff BH-55 (I think that's the name of it) or Acratech one. Expensive but they will keep your camera/lens rock solid and still and will last a lifetime.
I have a Gitzo carbon tripod. I bought it used (can't go wrong there - Gitzo lasts forever) and it's worth having a tripod that has an easy release mechanism for the legs. You don't want to have to spend ages getting the legs out and back in for a photo opportunity...
BTW: happy withe the 5D? I'm thinking about it but am worried about the 3.9fps vs. my 6.5fps on the 40D. ...and no integrated GPS is troubling me...what do you think?