Second Dan’s comments, except add Unitron (and Ice Planet – Evan’s also a fan), and I haven’t started hardcore collecting anything from Classic Castle or Pirates. Not saying I don’t love them / wouldn’t collect, but you can only buy so many things…
There are pretty diverse interests within our group. Every theme has some redeeming qualities. I don’t care for the Chima theme / minifigs as they are, but they do have some good parts / colors. Same goes for Friends (& Disney Princesses), in my mind. The color palette offered there is impossible to find elsewhere. And I’m sure there’s a market for LEGO Ariel, Cinderella, etc., although I can’t say I’ve researched it yet. TMNT, while I loved it as a child, doesn’t do it for me in LEGO for some reason. But even that has some potential if you’re looking for parts. Basically any licensed sets have potential to resell the minifigs (well, not Lone Ranger… nobody wants that stuff). If you do buy sets for parts and don’t want the figs, we could always talk about listing them in my store – Bricks On The Dollar does that for several of the PennLUG guys.