A PrC focused on giving sorcerers a way of increasing their spells known.
Weak Bab, bad fort and ref, good will, d4 HD.
Full spellcasting progression.
Not sure on skills yet.
At the first level you get the ability to learn new cantrips. I haven't come up with a good mechanic or such yet for this, but I was thinking 1000xspell level to learn a new spell to add to your spells known, though might make it a bit easier for cantrips since they're not exactly too powerfull.
at 2nd level you gain the ability to add 1st level spells to your known spells list.
And it goes all the way up to level 10 where you learn to add 9nth level spells.
As for requirements, I'm not sure yet, but they should be high, perhaps level 15 or so, though I don't know the specifics.
Input, suggestions, comments etc are very much appreciated 
If you are really interested in PrC's for sorcerers, there's an "official" one in Dragon magazine #280 (February 2001). It's called the "Eldritch Master" and was created by Monte Cook.
It's ten complete levels of Sorcerery (sic) goodness!