Spells/curses are a fun trope, because there are so many things you can do with it. Not sure why it's usually Dean who's the victim, but there are some good Sam-centric ones too. I'd rec Filibuster (Sam's cursed to talk without stopping), and And She Was (Sam's cursed with boobs).

I'm not much a fan of AU fic either--there's just so much in canon I want to read about! A/B/O isn't my thing unless I happen to be looking for a very specific kind of porn, but I can understand why other people like it. "Heat" is basically sex pollen, and if you've got a thing for excessively large penises, then the idea of knotting might be attractive. And lots of people like the idea of soulmates or 'love at first sight,' which is built into A/B/O too. And mpreg. Basically, I think it happens to combine a lot of iddy tropes that people enjoy.

I'd love to read an early season wincest fic by you, with lots of rich road trip stuff built into it.