These episodes are only in order of season, not of importance or rank. So, here are my choices for seasons 1-7. Seasons 8-15 will be part 2.
Season 1, Episode 4
If you think about it, this episode introduced three very important parts of lore that are relevant today. It was the first episode with demons, albeit might primitive compared to what they are now. Second, it was the first time that Sam and Dean put on the "monkey suits," aka the dark suits that would be needed to impersonate Feds, this time Homeland Security. Third, we learned Dean's greatest fear, which is the fear of flying.
Me, I loved the tone of this episode. It had some action, some brisk and funny dialogue, an engaging story, and a rather emotional ending. This is a frequent episode on my rewatch list.
A side note, I met writer Richard Hatem in a press room and told him how much I loved this episode. He told me he wrote this episode to over come his own fear of flying! So you see, writing can be therapy.
Season 2, Episode 7
The Usual Suspects
If I thought "Phantom Traveler" had brisk and funny dialogue, then this one puts that to shame! This is a very clever plot from beginning to end. It's Sam and Dean with their sharpest wit on display, and guest actor Linda Blair just made it exponentially better. Sam and Dean were in perfect sync the entire episode, and they weren't together in the same scene until the end. It contributed nothing to the lore or the overall scheme of things, but I find myself wanting to watch this one when scanning through season two.
Season Three, Episode Five
If you remember, season three got off to a bit of an uneven start. That's likely why this one gets so lost. But this is one of those better done "parallel" episodes, aka Sam bonding with the MOTW's father, relating their horrible situation to his own with Dean. It was creepy, it ruined fairy tales for everyone (totally a good thing), but it also showed how things were starting to unravel internally for Sam over Dean's demon deal. It was his first Crossroads Demon kill! Granted it was only a hint, "Mystery Spot" was the true episode that blew the one wide open, but in the meantime, I'll take a story about fairy tales gone wrong.
Also, when I see this scene, I die laughing every time. A classic Dean Winchester setup. Behold, Sam Winchester, the sketch artist.
Season 4, Episode 15
Death Takes A Holiday
It's hard to call anything from season four "unsung" given how explosive that season was. But I've always found this one gets lost in the shuffle when it comes to the lists. It's another really clever plot, it's emotional, and it involves some of my favorite lore, reaper lore. It had the fallout from "Sex and Violence," showing the growing brotherly rift. It really dug into the evil behind Sam's powers though and delivered the perfect forewarning for the audience anyway that Sam's growing power was not going to end well. Dean and Castiel had some cool moments in here too though, strengthening that story as well. I just thought this was a perfect setup to the next episode, "On The Head of a Pin," which is a series classic.
Season Five, Episode 7
The Curious Case of Dean Winchester
This is quite a Sera Gamble gem! I love this episode mostly because of the brilliant casting, let alone the enjoyable story. Not only did Chad Everett nail the essence of Dean as a senior citizen, but Hal Ozsan as Patrick the witch, the one that put Dean into this predicament, was also perfect. The fact that Bobby Singer was there stuck in the middle of all this Sam and Dean madness just added to the episode as a whole. In the end, we found out Sam was an amazing card shark. Is there anything this guy can't do? Well, aside from that one little malady that Patrick gave him.
Season Six, Episode 13
Oh my God, where do I begin? This is one of my all time favorite "Supernatural" episodes. It rarely gets a mention from most. It is dark. It's shocking. It's uncomfortable. It's also gripping and deeply emotional. Sam had to learn this about his soulless alter ego. The entire construction of this episode is brilliant. I hated the entire "noir" theme of this season, but it really worked here. The flashbacks were in black and white with the classic noir angles, each shaking present day Sam to his core, gnawing away at that unstable wall in his head. Dean's reluctance to help Sam, but being forced to do so anyway, led to some awesome scenes, especially the whole "momento" scene to trace back what happened. Jared just nailed just how disturbing each memory was. Who knew Soulless Sam was such a whore? The fact that every woman who crossed paths with him met their awful fate brought new meaning to "Sleep with Sam Winchester and die." As Sam was left reeling from the hopeless outcome of the case and the fact he was the cause of it, that was enough to break through that wall. Dean watching in horror as Sam collapses to the floor was one thing, but the memory of burning in Hell? I was screaming!!!
Season Seven, Episode 7.20
The Girl with the Dungeon and Dragons Tattoo
I loved Charlie as a character. This was a great introduction. She was just an everyday dork that found herself in the middle of some serious shit and took it on in her very quirky way. Dick Roman was actually entertaining in this one. It had a really fun caper that gave the team a much needed win. This was just a fun episode in a season where there was not much fun. There isn't much else to say about this one except "Peace out bitches."
Coming, my choices for seasons 8-15. What are your unsung heroes for seasons 1-7?