There are PanaVise tools both at my university's labs and at my job. For my home workbench, I got the low-profile head (304) and low-profile base (305). It looks something like this:

They're mounted on a 3/4" thick tray holder in that picture, but I've got a piece of 1/4" plate steel. I can rest my wrists on the bench, and solder to a PCB or wires held in the jaws just a few inches above the workbench, giving me very steady hands.

I use the nylon (insulated) jaws with a groove (to hold PCBs), but I'll warn you: when you're under the microscope, and the shaft of your soldering iron starts melting the plastic outside of the viewing window, there's a 3-4 second delay before the stench of burning plastic reaches your nose. A razor or Xacto knife will clean it up.

PanaVise is a popular manufacturer right now (2011), but there are and probably always will be other small, tilt/turn vises available. I feel that the sturdiness of a vise is of great utility when trying to do any work like this; those third hand tools can't hold any weight or pressure. The tug of the wire would pull them over. When tinning wires, you can insert a long row of them, instead of working one-at-a-time with the other tools mentioned.