Drill Guides -- The Forgotten Tool. 

Even though I own a set, I will still often forget to use one.... and always to my detriment.

Big Gator Tools makes what I consider the preeminent drill guides. No affiliation, sadly, but I have no problem recommending their product because it's solid quality, made in America, and more useful than you might imagine.

As a blacksmith, I often have to use a hand drill to make a hole because the workpiece is too large for the drill press. The Big Gator drill guide makes that job a lot easier and helps to guarantee that the hole will be oriented properly! 

They even offer "tap guides", a wonderful tool that helps make sure your tap is perpendicular to the work when you're trying to cut threads into a hole.  If you've ever had to hand-tap a few holes, you know how aggravating it can be -- especially when you get done and find out one hole is catty-wompus!

I can't say enough good about Big Gator Tools and their wonderful creation. If you don't have a set, get a set. You might only use them once a year, but when you need them.... you'll be glad you have them!