I kick everything to one side of the downstairs, vacuum, then kick everything back to the other side and start over. I also cannot keep toys picked (my 2-year-old dumps everything out even when my almost 4-year-old is actually picking up). Sometimes I put the kids at the table with puzzles or something while I pick up fast and they love to "help" vacuum by zooming around with a few push-toys.
I am considering putting a few types in lidded bins in the basement and swapping them. The problem for my kids is that they actually like and play with everything. They also remember and know if they can't find something specific. (The reason I can't really thin things out unless they are broken.)
For now, I have 2 3-drawer carts from Wal Mart (narrow ones) and used clear tape to put words and picture "labels" on them to help the kids sort toys, and all of the bottom three shelves on our bookshelves are for kids' things (books, large toys, dinosaurs, etc.). My floor is so rarely picked up that I usually take pictures when it is clean because it makes me feel better. The worst is getting the kids to help. It takes ten times as long to have them pick up than it does to wait until they're asleep and do it yourself. I know it is important for them to take care of their own things, but it is a lot more frustrating for parents.
This was more of an empathy reply than suggestions I guess. There will always be a mess, I am somewhat reconciled to that, but I try to vacuum at least once or twice a week anyway and kick things away from the main traffic areas.
P.S. / UPDATE
I might try Jamie M's idea and just leave out what I can stand. They do well with limited access things like crafts, but I also don't know what else I would put on our bottom shelves and I hate to leave them bare. :)