The best list? Probably sorcerer.
It depends somewhat on what you want to do, though. Clerics might have slightly better spells for buffing up and crushing people's skulls, and defending against/removing negative effects. And clerics can also access a lot of the better wiz/sorc spells via domains, alternate class features, etc. So I think it is probably:
1) Sorcerer
2) Wizard
3) Cleric
4) Psion
5) Druid
But clerics that cherry pick can get up to pretty much even with the wizard, and they automatically know all the spells on their list. Sorcerers have a few spells that are unique to them that are very good, but their limited spells known and slower progression is a huge drawback, IMO. Of couse, Runestaves and other such items can mitigate that, as can kobold cheese.
I'm not considering non-core stuff like Beguiler here, either.