I obviously won't recommend Dungeon, Inc since I'm the author, but I will point to some reviews of some of their modules that I really liked.
My favorite is Hounds of Hendenburgh, which I am currently running for my daughter and friends. Review is here:
The Horrendous Hounds of Hendeburgh by Liam Pàdraig Ó Cuilleanàin. It's a western fantasy flavoured sandbox with elements of monotheistic faith, faeries and witches. Lots of varied things that can be done, it's really worth the price of admission considering how many game sessions you can run just on this one adventure. My teenagers have currently entered the mines, and I'm really concerned there'll be a TPK, but I'm running it with DCC so with a bit of luck the spellcasters will roll high...
I liked Ragged Hollow as well but I felt it more centered on a core mystery which I couldn't imagine my inexperienced players could tackle effectively (right now, when a session is mostly spent gathering information and such, they apologise at the end for having "done nothing" ;-) With more experienced players though I think it's a really good pick:
Nightmare Over Ragged Hollow by Joseph R. Lewis
As for Knock! I own them all but I haven't read them all by a long stretch. It's the kind of thick zine that you flick through and read an article here and there, or get an idea from a random table, or even read a bit of mini-dungeon and go "ooooh, I'll know what I'm running as a side-quest next month". The vibe is very OSR but really the material is relevant to anyone playing D&D or derivatives. Some articles on play styles and early approaches to RPGs have really opened my eyes to what was happening at my table as well.
Finally, Black Sword Hack is really cool. It's the easiest toolkit to run a Moorcock style game, but it's not limited to that, I don't think. I haven't run it but I played in a couple of games and felt it ran really smoothly and stayed fun at all times.