Some PE I'd love to see..
Sorcerer Master of Magic Missiles. (Dragon Magazine Compendium PRC page 80)
The first PE you get gives you an extra missile with magic missile, chain missiles and any other varient of magic missiles. You also have a metamagic ability now that changers their elemental. (thus allowing you to do fire, ice, acid, or sonic damage)
The second gives you another magic missile, and gives you a 30% chance that you will break through anti-magic missile protections such as Shield and Shielding brooches. You also gain the Swift shield power. (allowing you to cast shield once per day quickened.)
The third gives you the last magic missile, making it a total of 8, increases the chance to 60%, Your shield spell has a 30% chance to reflect MMs back at the enemy. Magic missiles are also auto-still spelled.
Ultimate Magus (Compleate Mage)
Can only be done while multiclassed between a wizard and sorcerer (and doesn't allow you to have their PEs)
Long story short, by the end of the chain of enhancements you will cast as though you were level 15 spell caster in both, but you only gain spells up to either 10 or thirteen for both of them. Meaning you won't have access to top level spells.
Mystic Thugue (DMG)
Same thing as Ultimate Magus, but you can get it by MC between a Wizard or Sorcerer and Cleric or Favored Soul.