Versatile Spellcaster

(Races of the Dragon, page 101, DnD 3.5)

[General]

You can use two lower-level spell slots to cast a spell one level higher.

Prerequisite

Ability to spontaneously cast spells

Benefit

You can use two spell slots of the same level to cast a spell you know that is one level higher. For example, a sorcerer with this feat can expend two 2nd-level spell slots to cast any 3rd-level spell he knows.