My first roguelike was Ragnarok which did not allow a character with the same name as one already in the high score list (at least I think that was the criterion) and instead picked a random name, so I got into habit of never reusing the name. I have seen somewhere a system of naming characters like Zeno I, Zeno II, Zeno III etc., which makes the highscore list meaningful (but I think it did not work correctly).
Myself, I try to come up with some low quality pseudorandomly-by-hand generated name matching the character type. Sometimes I create names by sequence, like Aruung, Bruung, Cruung, Druung, etc.