My top 5:
Multimeter: god at the shoddy wire runs i would have went insane over if i didn't have one to test things out with. Such an invaluable tool not only in the car but aroudn the house.
Wire Cutters: keep a few various sets around with me, a few snub nosed with long handle for the 8 - 2 gauges, and a normal pair like Will had in the 2nd pic for the smaller gauges. Also carry a small razor blade to cut insulation on the big gauges.
Soldering iron: Not just for soldering! Sometimes you get that client whose old dash plate was just a wee bit sun warped, and theres no way in gods name i am bending that fragile plastic without having a little give in it, ;) Great for the heatshrink for your splices after your done soldering thing up... and the occasional time where somehow, you've misplaced those wire cutters, :eek:
Assortment of bits and hand tools: Sure wire cutters are hand tools, but with as many as they make, and as valuable as they are, they get a cat of their own. My kit has suck things like: torx bits, star bits (with saftey punch) 90 degree screw drivers (for those tight spaces), sockets and drivers, as well as the usual screw drivers. When you start messing with all the manufacturers various ways of doing things, your learn quick that they can be screwey with things.
Cleanups: Split loom, zip ties, fasteners, and the likes. When i get done i want my install to look like it rolled off the line that way. No shortcuts. It may have taken an extra 30 minuites to fish the wire in that manner and fasten it under the dash.. but did you know it was there till i told you? Didn't think so, ;)

