These days I'm inclined to think of traditional slip-joints, such as GEC and Moki, when I think gentlemen-carry. I'll also echo the mentions of Mcusta and William Henry. Of course, you can also go with a small auto, legalities permitting. My Protech Don, though not that small, but very slim and light, has been my go-to "formal" knife for awhile. Perhaps not that office-friendly though....