I used a Really Right Stuff BH-25 for my spotter and always worked perfectly. Hard to beat the weight of it as well.
I have one of these and I second the recommendation. You can pay a little bit less, and get a whole lot less, than what the RRS head delivers.
Unless you need a lever release, I recommend buying a bare ball head from RRS and then adding one of the generic Arca clamps available on Amazon.com; that and a generic Arca compatible plate will complete the setup. Should be able to get it all for around $150.