I've been asked to recommend a good small ball head that would work well with the Pico Flex Dolly or a good one for small sliders. I tested out a few, and the one that seems to fit the best is the Fancier FT6691. It's larger than the Giottos mini ball head, but still smaller than the larger Fancier Ball head I often use with the Konova Slider. For the price, it's a perfect little head for even DSLR cameras giving you extra stability with your sliders or table dollies.
All metal with strong clamp force to keep the camera in position and a quick release plate (with safety latch) so you don't have to spin your camera off. So far I haven't found anything else that offers this type of bang for the buck. If you've got suggestions for a good similar feature ball head, let me know. Floating around $24 dollars, you can find them over at eBay (click here)
Fancier Small Positionable Locking Camera Ball Head - via eBay
Cheaper and available for Prime shipping over at Amazon below (click here)
Fancier Small Camera Ball Head - via Amazon