D'Addario Micro Headstock tuner; also seems to be sold as "Planet Waves PW-CT-12 NS Micro Headstock Tuner".
So affordable and convenient that I have one for each uke that I use regularly.
I keep one on each of my ukes. I did get one that was a dud - emailed the company, gave them the information on where and when I bought it, and (with the help of a magnifying glass) the numbers on the back of the unit (It helps them track and see if it was a bad batch, or just one that was bad). Two days later, a brand new tuner was delivered to me.
As opposed to the Snark tuners I started with, that - while very accurate - ate batteries, broke when you looked at them funny, and I find very distracting when I see them on a headstock (I've seen many pro musicians have them hanging off of their electric and acoustic guitars, banjos, mandolins in concert.). I've got a Korg in-line tuner somewhere that I bought 30-something years ago, but the only instrument I had with a pickup back then was my shallow-body Ovation Pinnacle guitar, and I had removed the battery, since I didn't own an amp. I should probably find that Korg for when I start gigging again...
-Kurt