Dark Ritual was banned for as long as I remember (I played extended during 2003-2006). It's pretty much the definition of an OP card: if you were to draw 2 copies and a strong creature it'd be almost imposible to lose that game.
It's interesting to note that when the ability to produce a lot of quick mana with a sorcery was shifted to Red, two of them (Seething Song and Rite of Flame) also got banned (in Modern).
Interestingly even the third most powerful boon is powerful enough to be a multi-format all star.
The last two of course... are not.