http://thecentercolumn.com
Check the system tripod rankings. You can sift the options down to a few results based on the price, size, and stiffness specifications.
I went with the FLM CP-34 L4. It's under 24" folded, and it stands well above head height extended. That's super useful in situations where you want to get the camera above traffic/crowd level.
I recommend using a good lens foot, an L-bracket, a tilt/pan head, and a leveling base.
Pan/tilt heads have minimal sag and won't shift as much as a ball-head when you tighten them down. However, they aren't self leveling, and aren't designed to be pitched 90º sideways. For best results, they need to be used with a L-bracket (to get portrait shots when you don't have a lens foot) and they need a leveling base (so that you don't have to futz with the tripod legs.
I just picked up the Arca Panoramic head. It's similar to the long-lens head, but has some minor tweeks specific for panoramic photography. The clamp can be rotated for use with a l-bracket or a lens foot without tools. That was a big issue with my previous Sirui pan/tilt head. I highly recommend it.
This setup is rock solid. I use it with the 200-600, a gripped body, and a teleconverter. Also works for astro with a tracker.