I'd like the initials to be in the form of a monogram or better yet, a cipher (i.e., a monogram with the letters intertwined).
These are likely to be printed in a single color, but I'd consider a two-color design if it's really striking. The color I'm most likely to use is navy blue. Secondary colors would be maroon, white, or black.
I'd like something personal, unique, and masculine.
A few years ago I designed a cipher for my wife (really just a sketch, and I'm no artist) and sent it to a letterpress printer as an example of a design to put on notecards for her. She thought the design would look interesting and personal as-is, and so scanned the thing and cleaned it up; we went with that. I've attached the sketch and a (poor) photo of the printed notecard.
The notecard itself, and the concept of the cipher, is what I have in mind for myself here. But I am not married to the idea that the initials should be in that order (with last name in the center) or that they should be in a circle. I'd also note that I consider the example slightly feminine -- something bolder or more masculine would appeal to me.