Every episode has them! Golden lines that run 'round and 'round in my head. Here are some that have stuck with me! (3 from season 1, 2 from season 2, so there could be a slight spoiler if you're very picky.)
Chin: You did pass the HPD Test for pursuit driving, right?
Kono: There’s a test?
1x14 He Kane Hewa'ole (An Innocent Man)
Danny: I can't leave you alone for two seconds.
(After Steve jumps off a building while chasing a suspect and lands on the Magic Rotating Balcony. Ask if you need an explanation.)
2x16 I Helu Pu (The Reckoning)
Danny: You couldn't walk him down the steps? (After Steve shoots yet another bad guy)
Steve: What's in his hand, Danny? He drew his gun on me, okay?
1x15 Kai e'e (Tidal Wave)
Kono: Thanks Fong, you're a geek god!
2x08 Lapa'au (Healing)
Okay, while many of the best quotes make me smile, this last one has always been heart-wrenching to me. ::wipes away a tear::
Steve: You know, I never would have left the island, I never would have joined the Navy, or missed every holiday, every birthday, half of Mary's life. The day that car exploded, that made me who I am. Danny, I can’t just let it go.
1x13 Ke Kinohi (The Beginning)