Quoted from CLEllison:
Who here owns the extended versions of the movie? If not please reward yourself and get them.
Yes! I own the extended blu-rays. It's certainly a must to watch them indeed! All 3 movies have extended scenes that are worth watching, from the market scene where Bilbo buys his dinner trout, to the Goblin Town King song, to the rolling chariots with automatic crossbows! The extended dialog with Beorn is also great, as it explains why he ends up participating in the final battle.
Edit: Oh, and let's not forget the actual fight between the Elves and the dwarves from the iron hills. The dwarves have clever machines that stop arrows in mid-flight. Fantastic.