Well, since I just bought this today, and I know I'll get a lot of use out of it (I've been borrowing another mechanic's multimeter at my shop regularly) I'll say my multi-meter:
[Linked Image]

I also have to cast another vote for my leatherman. I have a pair of needlenose pliers that sit un-used in my tool box, since I always grab my leatherman first. I use it daily.

and a third and final vote for my Streamlight Stinger flashlight. There's nothing I hate more than trying to work on something I can't see.