Favorite Harbor Freight Tool, bar none:
The Electronic Fly Swatter.
Absolutely essential equipment in any garage that has hover fly's hovering around to escape the outside winds. There is nothing quite more satisfying than playing tennis with those flys, and hearing that SNAP! and seeing the smoke from one of those pests being cooked. Black handle, yellow tennis racket looking thing, $2.79 right now with coupon, $3.99 on sale, $7.99 regular price. Not much else Harbor Freight is good for, but this fly swatter rocks! It works too!
Not sure if it's my "favorite", and I don't own many HF tools (but starting to come around for
some things) but I have to second the electronic "tennis racquet" flyswatter.
My father in law always picks up little *inexpensive* (or
cheap; but there is a distinction) things that end up being gifts for me. I thought this flyswatter was going to be a piece of junk, but damn, if it doesn't do exactly what it's supposed to. I agree on the SNAP when you get one - very satisfying.
Also would have to agree on the little multimeter. It was one of those things that I never got around to buying, because I always research the heck out of things and end up buying something way beyond what I need. Since this was a Christmas present from my father in law, it got filed into the same mental bin as the flyswatter, until the first time I
needed one, and remembered he got me it. Used it many times since, with no complaints.