Hello All,
I think the best
portable mouse, by far, is Kensington's Bluetooth Pilot Mouse Mini. Although it only has two button plus the scroll, I find it to be ergonomically superior to anything else I've seen. It's not too small to be comfortably useable, but it is small enough to be quite portable.
Best of all, it can be configured with Kensington's Mouseworks software. Kensington was very quick to release a UB version of this software, and it allows total configuration, on an application by application basis. Very nice.
Scott