+5 Holy Avengers go right back to the original AD&D 1st edition DMG. They're exceedingly buff weapons, and tend to be +2 or thereabouts in the hand of a non-paladin. Unearthed Arcana introduced a +6 Holy Avenger, which is just about the most obscenely broken standard magical weapon the game has ever seen. Holy Avengers are back to +5 only in the second and third editions. One feature of the Holy Avenger which is sometimes missed is that it is a holy sword, thus activating the Paladin special power involving such items. The Complete Paladin's Handbook includes a number of other holy swords.