I posted up about a very effective (and cheap) Velbon fluid head a few weeks back and it literally sold out in a few hours. For around $26-29 dollars, it's a great way to add on a dedicated Fluid head for camera dollies, sliders, etc. You can find the original video, article, and other comments about the fluid here: http://cheesycam.com/cheap-velbon-video-fluid-head-review/.

A few of the units are back in stock at B&H (click here).

Velbon Fluid Video Tripod head - via B&H

or at Amazon (click here) available at both B&H and Amazon (click here)

Velbon Fluid Video Tripod head - via Amazon