I've got various guitars in various different tunings. My old Korg DTR-2000 tuner had a handy function where i could press a button and it would transpose down a step the more I press it so no matter which guitar i held i could easily tune in as (F#)(B)EADGBE and the drop-D equivalents are burnt into my brain after all these years. All i needed to remember was how many steps down-tuned the guitar was and i was away.
The feature i'd like is a transposition mode on the tuner so I can turn a dial down to -3 and i can quickly tune into BEADGBE instead of having to figure out that i need G#C#F#BEG#C# which is a bit harder to remember. 
As a bonus related feature request it would be nice to select whether the tuner uses flats or sharps. I tend to think in flats by default so I always have to do another mental calculation to translate sharps into flats.
At the moment i've got another signal route going through my non-kemper rig and i'm actually switching that on just to see the notes on my old tuner.