Dean's little smirk as he walks away after the "Don't objectify me" line is so JA, really, but I love it.
Here's my S1 list, after much careful thought.
The pilot: It sets up everything you need to know so perfectly – Sam clutching at normal with both hands, Dean blindly faithful to the life his dad has trained him for, and his dad, plus brother tussling, paper clip porn, the first bitch/jerk exchange, Dean’s smart mouth and Sam’s earnest concern, and the bookend of Dean saving Sam from a fire again, and Sam signing on for vengeance.
Home: Not just for Missouri, although she’s a big part of it (as well as the shot of John at the end). Sam’s dream visions, the way Dean freaks out but won’t show it, Dean’s call to John, the backstory we get with them digging into their own childhood. Such a hurty episode, especially with them saving the kids.
Faith: Dying Dean! Wan, weak Dean in a Sam!hoodie! Sam fighting to save his brother, and Dean, as always, pretty sure he doesn’t deserve to live. Plus it’s the first time we see them dealing at all with faith and God, which is interesting, especially now. Dean’s interaction with Layla was pretty sweet, too.
Shadow: So much good brotherly ribbing and interaction in this one, and then Meg, of course. Also, scary! The daeva was vicious. Plus, the reunion with John, which chokes me up every time.
Devil’s Trap: The gang’s all together again! But oh, the angst. The cabin scene breaks me into tiny pieces, JDM is spectacular (they all are), and the final scene was one of the most evil cliffhangers I’ve ever seen.