Arcane thesis (Player's Handbook II)
One chosen spell has decreased spell-slot cost for each metamagic applied.
Choose one arcane spell that you can cast to be your thesis spell. [...] When you apply any metamagic feats other than Heighten Spell to that spell, the enhanced spell uses up a spell slot one level lower than normal.
Easy metamagic (Dragon Magazine #325)
Decreased spell-slot cost for one metamagic feat.
Choose a metamagic feat you already have. When preparing or casting a spell modified by that feat, lower the spell-slot cost by one. You can never reduce the spell-slot cost below one level higher than the spell's actual level.
Eldritch corruption (Heroes of Horror)
Apply metamagic, damage allies' constitution score.
You can enlarge, extend, heighten, or widen a spell, as though you had the appropriate metamagic feat, without increasing the spell level or, for spontaneous casters, casting time. You can apply any number of these metamagic effects to a spell in this way; if you choose heighten, then that spell's level is heightened by up to two levels. For each level of metamagic you apply, one of your allies takes 2 points of Constitution damage. In this case, "ally" is defi ned as someone who knowingly and willingly fi ghts alongside you against a common foe, or who otherwise considers you a trusted companion. You decide, when casting the spell, which ally takes the Constitution damage. You cannot select an ally immune to Constitution damage or an ally without a Constitution score. For purposes of this spell, you cannot designate a summoned or charmed being as your ally. You can use this feat three times per day.
Forceful magic (Dragon Magazine #308)
Once per day decrease metamagic spell-slot cost by 1.
Metamagic School Focus (Complete Mage)
3 times per day, decrease metamagic spell-slot cost by one for school of your specialisation or Spell Focus.
Choose a school of magic for which you have the Spell Focus feat, or the school in which you have specialized. Three times per day, you can reduce by one level the cost of a metamagic feat applied to a spell of the chosen school. If you prepare spells, you can have only up to three such reduced cost spells prepared at any time.
Metanode Spell (Champions of Ruin)
Decrease metamagic spell-slot cost depending, by value depending on the layer and class of an earth metanode in which you stand.
When casting a spell improved by a metamagic feat, you can deduct the class of the earth node layer in which you currently stand from the increased spell level. (The class of the layer does not equal the class of the node unless you are standing in the innermost portion of it.) For example, if you use Maximize Spell to augment the 3rd level spell fireball in the innermost (+1) layer of a Class 1 earth node, you cast the spell as if it were only two levels higher than normal, not three, because the earth node pays one spell level's worth of the metamagic cost. This feat is most useful to casters who do not prepare their spells (such as bards and sorcerers) and to wizards who rarely leave their earth nodes and can therefore prepare and cast their spells at the adjusted level.
If you use this feat to reduce the cost of preparing a metamagic spell and then leave the earth node, the spell you prepared becomes unavailable until you return to an earth node layer of at least the same class as the one in which the spell was prepared
Metaphysical Spell Shaper (Book of Erotic Fantasy)
Get ability damage for applying metamagic feats and decrease metamagic's final spell-slot cost by 1.
Metamagic Manipulation (Su): At 1st level, a metaphysical spellshaper
gains, the ability to cast metamagic spells spontaneously by taking
ability damage instead of increasing the level of the spelL He chooses
which of his ability scores to damage. All damage from a casting of a
spell must go to the same ability.
Metamagic Mastery: At 3rd level, the metaphysical spellshaper reduces
the final spell-level slot required by metamagic feats by one (to a
minimum of one).
Halruan elder (Shining South)
At 1st level and every 3 next levels decrease the spell-slot cost of chosen metamagic feat by one to a minimum of +1.
Adroit Casting (Ex): The Halruaan elder has become so skilled at casting his spells with various metamagic feats that utilizing such feats has become easier for him. At 1st level, he picks a metamagic feat he knows. The cost in increased level of spell slots to use that metamagic feat is now permanently reduced by one level, to a minimum total modification of a spell's original level + 1. For example if a Halruaan elder with adroit casting 1 wishes to prepare an empowered magic missile, that spell takes up a slot only one level higher than its original level (instead of two). At 4th level, and every three levels thereafter, the Halruaan elder can choose another metamagic feat he knows. That feat gains the same benefit; spells altered by that feat take up a slot one level lower than normal (minimum of the spell's original level + 1). If the Halruaan elder doesn't have a metamagic feat to apply the ability to when he gains a level that grants adroit casting, or if he's has previously applied adroit casting to all of the viable metamagic feats he knows (any metamagic feats that require spells to occupt a slot two or more levels higher than normal), he gains no benefit from this ability until he aquires a new metamagic feat that adroit casting can affect. At that time, he can automatically designate that feat as altered by the unused application of adroit casting.
If you are interested in applying free metamagic to spells I'd recommend to read this article.