Complete Mage, Complete Champion.
They're basically at will-spell-like abilities, that function, as long as you can cast a spell with a certain descriptor, and the power depends on the spell level of that spell.
For example, one feat (Fiery Burst) allows you to sling mini-fireballs, with 5 feet-radius, doing 1d6 fire damage per spell level of the highest available spell level.
For example: You have prepared a fireball and a scorching ray. The fireball is a 3rd-level spell, hence your Fiery Burst deals 3d6 damage (in 5'-radius) - until you cast your fireball.
Then your highest level fire spell is Scorching Ray, hence the Fiery Burst will only deal 2d6 fire damage. When you've cast the scorching ray (in this case your last fire spell), you cannot use Fiery Burst anymore.
I hope that clears up the whole stuff.
Cheers, LT.