I use photo album replacement pages; the ones with reuseable sticky stuff and a plastic film over it. The can be found in WalMart. The have a front and back, so you can put up to 10 overlays on a page.
I've had success using baseball card plastic page protectors. They have slots for 9 cards per page and can fit most of the standard size overlays. The large ones I place in other kinds of page projectors.