You got me
El Kapitan: you have me on the Disney stuff - none of the nearly 2000 Lego sets I've bought over the years has "Disney" in its name or category.
Others mentioned the Harry Potter sets as specialized. Well, a local friend who has the largest online LEGO store in Canada called them "Harry Parter" since some are such a goldmine of parts for other stuff. I don't have an online store, but bought multiples of some of them to get the parts.
I like the modular buildings, and some of the Creator 3-in-1 sets. I also buy boxes of just bricks, but for larger quantities I buy on bricklink.com . I love large Technic sets, but find the new lift-arm style ones a pain (physically!) to take apart.