Funny you should mention Toy Story as not one of the more popular categories; I loved Toy Story from the beginning and decided to collect from that movie (and Monsters, Inc.), so I have tons of pins in my collection. All of a sudden, when TS3 was released, TS pins became a LOT more popular. Where once I usually didn't have problems trading for TS pins, I do now sometimes.
Stitch is still really popular after all these years, but nothing beats the insanity of those early days. I don't collect him specifically (I have some pins I like with him), but I think back to "Stitch Sundays" at DLR and remember the Stitch collectors going crazy, lol!
Tinker Bell seems to be consistently popular too, and HM, and NBC, and Jessica Rabbit. For a while (before the movies and during), POTC pins were really popular too, and I remember some were very hard to get (the attraction), and also Malificent. Pins with Walt used to be gold; I don't even know anyone who avidly collects Walt pins these days. Blue Fairy was pretty popular too, and so was Jiminy Cricket. Does anyone care about those two today? LOL! And CM pins (the ones only they could buy) were really popular, not as much now, but then, the designs seemed to be a lot nicer then, now some are, most aren't. No one I know of is (or rarely is) driving a hard bargain for a CM pin, based on that fact alone.
Of characters that have been around for a while (not "newbie" characters and movies such as Tiana, UP, etc.), Alice seems to be far more popular now than when I started. It's been interesting to see the collecting trends all these years!