Didn't we have a list somewhere on this? If not, hell I'll throw it in Class Boosters.
Feats
Snap Kick (ToB): +1 attack, -2 to attack rolls, not full-attack dependent.
Planar Touchstone[Oxyrhynchus](PlH): +1 attack, -5 to attack rolls, works anytime you deliver more than one attack (see snap kick).
Two-Weapon Fighting (Core): +1 attack, -X to attack rolls, full-attack dependent.
Improved Two-Weapon Fighting (Core): +1 attack (total +2), -X to attack rolls, full-attack dependent.
Greater Two-Weapon Fighting (Core): +1 attack (total +3), -X to attack rolls, full-attack dependent.
Items
Speed (Core): +1 attack, full-attack dependent, doesn't stack with haste.
Maneuvers
Flashing Sun (ToB): +1 attack, -2 to attack rolls, only works on a full-round action.
Dancing Mongoose (ToB): +1 attack, +2 if twf, uses a swift action, not full-attack dependent, once per round.
Raging Mongoose (ToB): +2 attacks, +4 if twf, uses a swift action, not full-attack dependent, once per round.
Spells
Haste (Core): +1 attack, +1 dodge to attack rolls, full-attack dependent.
Classes
Frostrager (FB): +1 attack, -2 to attack rolls, once per round and not full-attack dependent.
Whiling Frenzy Barbarian (UA): +1 attack, -2 to attack rolls, full-attack dependent.
Monk (Core): +1/+2 attacks, -2/-0 to attack rolls, full-attack dependent.
Shadow Pounce Granting PrCs
Sun School (CW): honorable mention, +1 attack after you teleport, requires bab +4 and furry of blows so ECL 5 is multiclassed.
Crinti Shadow Marauder (SS): obtains shadow pounce at the 5th level, requires 8 skill ranks to enter so ECL 10.
Telflammar Shadowlord (UA): obtains shadow pounce at the 4th level, requires 10 skill ranks to enter so ECL 11.