Erudite Addendum: Due to a rereading of the base class' Unique Powers/Day ability, it is possible that even the base Erudite is capable of being Tier 1. Access to all non-Discipline/Mantle Psionic Powers of 9th level and lower (and able to learn any Mantle/Discipline power of 8th level or lower) means it has the spellbook ability of the Archivist, but Psionic-only. The Unique Powers ability is somewhat unclear, but RAW says it is 11 powers/power level, not just a flat 11 powers. This means 11 1st level powers, 11 2nd level powers, and so on.
Furthermore, the ability to select unique powers/day on the fly is like a Wizard with Uncanny Forethought, only more uses/day and no Full Round action or CL penalty. This is, effectively, the most versatile class ever printed in terms of spells/powers alone (the Archivist still needs to prepare each day, the Wizard is limited when using Uncanny Forethought and only has the Sor/Wiz list unless he uses feats/PrCs to add spells, and the Artificer needs to craft items in order to have the same kind of flexibility).
The Erudite is capable of "learning" a spell as a full round action. In 16 hours worth of time, AKA 9600 rounds, he is able to leech an effective 9600 spells. He can "write them in his spellbook" merely by sleeping for 8 hours to recharge his PP and paying 20 XP/Erudite level/Power he wants to learn, and can pick and choose from those 9600. What this translates into is he can learn 50 new powers by forgoing a level up, the same way a Wizard can stall their own level up to craft magic items (DMG, I forget the page number, but it is in there).
Due to the RAW on his Unique Powers/day, the Erudite is not as restricted when multiclassing as we first thought. An Erudite who multiclasses at 6th level has 4 unique powers/power level, effectively the same number of spells prepared as the unmodified Generalist Wizard, but the spontaneity of the Uncanny Forethought feat on crack. There's also an advantage to multiclassing out at an early level: the cost to learn new powers is set by your Erudite level, not character level or manifester level.
An Erudite 6/Anarchic Initiate 10/Slayer 4 only has to pay a grand total of 120 XP per power he tries to learn; compare to an Erudite 20, who has to pay 400 XP per power. The advantage somewhat outweighs the restrictions placed on the Erudite's manifesting abilities. An Erudite 19 who forgoes gaining his 20th level can learn an effective 50 Powers of his choice, all within 24 hours. It takes him 5 minutes to leech these powers (though he can't manifest anything during those 5 minutes). The XP the Erudite forgoes is 19,000 points (20*19=380. 380*50=19,000), which is enough XP to gain a level.
Contrast with the Erudite 6/Anarchic Initiate 10/Slayer 3, also a 19th level character trying to level up to 20th. He has 19,000 XP to spare, and a free day's worth of time. The cost to learn a power for him is a mere 120 XP, which allows him to learn approximately 158 new powers at the cost of gaining a level (19,000/120=158.33, rounding down to 158). 158 rounds is 948 seconds, or 15.8 minutes.
Adding in Spell to Power or Dragon 349 only makes things more ridiculous, as it opens up entire new spell lists for him to leech from. This can arguably push the Erudite into "Tier 0".