Alternate Class Feature! Its a way to trade things out! For example, you could...
....Trade your first favored enemy for favored enemy: arcanists, from complete mage
....change Ride as a class skill for Tumble, from the cityscape web enhancement
....change wild empathy for the ability to cast speak with animals or speak with plants, as a spell like ability, from Complete Champion
....Trade track and swift tracking for a rogue's trapfinding, from Dungeonscape
....Trade animal companion for a trick with ranged weapons, from PHB 2, or a particular type of familiar, from the cityscape web enhancement, or having your favored enemies work on to hit and damage, from dragon magazine #347
....Swap the standard combat styles for a few more varieties of combat styles, from Dragon Magazine #341
....Replace the combat styles entirely for Wild Shape, from Unearthed Arcana or the SRD
....Change most of the progression of Ranger to be a Mystic Ranger, who is much better at spells, from Dragon Magazine #336
And there are even more, if you know where to look! And further... most of these can be combined!