I'd really like it if my digitech multifx pedal had tap tempo for delay. That's one bad thing about using an "all-in-one" pedal. So inconvenient to change settings of different effects on the fly :\
External tap tempo pedals are easy to make. All you need is some wire, a jack and cable (or just a cable if you want to wire it directly), a switch, and a box to put them in. Altoids cans work :3 Solder is nice but not actually necessary.
I forget what type of jack and switch is required, though.