My girls got a toy organizer for Christmas. It has 3 shelves with 12 bins. I think it's selling for $60 at Target right now; we got it on sale right before Christmas for $27. I like it a lot. I'm very particular on things being sorted because otherwise my girls (ages - 4 1/2, 3 and almost 2) complain they can't find certain little pieces later on. So, they can take a bin out and play with it, but I make them responsible to put the right pieces away or they'll be the ones looking through the bins later when they want/need something. Of course, my almost 2 yr old doesn't do so well with the sorting, but she is aware of which bins she can play with - none with the small POlly pocket or littlest pet shop pieces. So, that helps for her toys, too.
I don't rotate toys; I go through the girls' toys every couple of months and give away the ones they haven't played with in those months....which always tends to be more than I imagined. They are constantly getting new toys from people and Grandma :) for birthdays, holidays, etc....so, it's not like their toy collection is dwindling....ever!
I do help them pick up when they've made a huge mess with my youngest, but if it's just a bin or 2, I let them know they made the mess so they can pick it up. My helping with the big messes is just because my youngest doesn't quite get the sorting system.
At preschool, I know they have to pick up after themselves, so I think it's only fair that they do that here in their home, too
Good luck. Toys can be so frustrating sometimes! :)