Ogmund's Tomb: a Nord dungeon/ruin just across the river from Riverwood. I really enjoyed this one: a band of bandits who turned religious, who got more than they bargained for when they delved deeper into the dungeon..
Like true Skyrim fashion, the story is told in notes and letters found on dead bodies, and through journals. Loot is pretty good, but in keeping with the challenges, and the environment is varied and lively. This could easily have been an 'official' dungeon.
In Search Of Hrongar's Ring: again, a Nord dungeon, just north of Whiterun. The quest starts when you talk to someone in Candlehearth Hall in Windhelm, and is a simple quest to loot a particular item off a draugr in a tomb.
I didn't really like this one: the halls in the tomb are too big, the challenges are minimal, the loot overpowered. The way back from the end boss to the exit is like a long tunnel interspersed with too many burial urns. Now, don't get me wrong: I really like looting the gold and jewels from the urns, but it's more like five chambers of this:
If you're looking to make a quick buck, then this is for you. Otherwise, the appeal is minimal.
No Mercy, by prolific modder thirteenoranges. A lovely little quest about the conflict between a nest of vampires and a chapel dedicated to Stendar. The end is, literally, a dungeon crawl: don't forget to bring a torch or you'll have to blunder about in the pitch black!
High-quality surroundings, nice little side quest with good loot and an interesting boon at the end. Recommended!
Sea of Ghosts, another one by thirteenoranges. At the Solitude docks, you can hire a ship that will take you to various islands across the Sea of Ghosts, north of Solitude. There's also a player home for sale.
The quest is fully voiced -- though there's only a few lines of dialogue, it's still a nice touch. You can hear that the amateurs didn't have a full recording studio at their disposal, but that's only a minor quibble. The locations are varied: there's some rocky shallows, a small island with a lone house on it, a Dwemer ruin and so on. It reminded me a bit of Myst: isolated islands that contain a small quest or puzzle. And there's a side quest that has you find a northern outpost of the Blades too.
The environment is really nice. Especially the cave with the geode veins at the 'lone island' are lovely. Challenges are good, and the loot is balanced. Thirteenoranges likes climbing apparently: there's a lot of jumping up mountains or the sides of a cave to get somewhere -- which is something that is almost absent in the 'vanilla' Skyrim, so that's an interesting addition. And the view from up above is lovely:
I didn't find the player home that interesting, but the rest is really nice. Recommended as well!
Helgen Reborn: You chance to rebuild Helgen after Alduin destroys it in the prologue! You get to assist a band of Thalmor-hunters(!) into reinforcing Helgen as their base of operations. You can even choose to make it an Imperial, Stormcloak or independent city. You get to train recruits, visit a whorehouse and fight against the Thalmor.
It's fully voiced, which is nice. The questline makes sense and has you travel all over Skyrim, and the apotheosis has you wiping out a Thalmor nest. After that, you get your own private tower (and a special display cave underneath), and the city is slowly rebuilt into a thriving village with lots of shops. Very nice mod, with good tie-ins to the background story of the game.