Feats are the most expensive and useful commodity in D&D, and if you can get them for free, it is incredibly useful. Now, we all know the Otyugh Hole, the less useful Alertness from a Familiar/Psicrystal/etc, and the Masterwork Lute/Vest of Legends trick. The issue is the last two aren't permanent and aren't very useful.
So, that leads us to the question how else can you get free feats? Or, more importantly, permanent feats useful for anything other than shuffling?