I think that in a way Berserk and Vagabond have some interesting similarities in their protagonists, which seem both the same kind of (self chosen) outcasts to me. Vagabond always has to be recommended, but I specifically recommend it to people who like Gatsu - he has a good load of similarities, while beeing absolutely different in other ways, too.
Focussing more on a psychological aspect, I also see Kokou no Hito beeing a little similar in the protagonist (although the scenario is totally different - modern time, civil life story) as well as Wolfen Crest. The similarities seem really far off, but all of these have the same kind of Lone Wolf Protagonist.