The Ritual of Rebirth is the only reliable way to bring a hero back. If somebody's presence is still strong enough on this plane (i.e. they are still famous enough to be on the Hall of Fame) then the Death magic spell can bring them back as a mummy.
The mummy-Version is almost identical to the original. It has a few new advantages and a few new disadvantages, but is sometimes a bit more powerful. Just keep them away from open flame!
The only other way I can think of would be to use Wish, and I've never tried wishing for a specific hero. Wishing for a "Hero" in general gives you a random one, and it'll be a unit instead of a commander until you Gift of Reason it. Paying 100 Astral Pearls per try at the Big Slot Machine of Destiny seems ridiculous if your trying for a specific hero, and I'm not actually sure the game will allow redundant commanders through that approach.
[ March 22, 2004, 19:14: Message edited by: Psitticine ]