Workbench with a Vice
This may not count as a "tool", but not having one can make DIY projects difficult. I don't have one, and trying to sharpen a mower blade on your kitchen table is sub-optimal. Then there was the metal bracket I needed to drill a hole into... holding it with my hand...
I've had my eye on this bench from Home Depot. I like the steel work surface. I will need to drill holes to bolt the vice to the top, though.
Update: Last weekend, I bought this bench along with a 6" vice. My dad and I assembled it as a weekend project. We drilled holes for the vice and secured it with 1/2" bolts. Overall I am pleased with it. It did require a drill for assembly, which was a little unexpected. Here are the photos. (Sorry for the poor lighting, a good workshop light is next on my list!)