Trundle Beds! These things are awesome. It is basically storing one bed under the other. This is great for kids rooms or an office where there is room for a day bed.
Bunk Beds maximize the sleeping space and floor space at the same time. With the extra floor availability you could potential have two sets of bunk beds. Just put them on opposite sides of the room. Your guests' children may figure out how to jump from one to the other. Ha! I would have tried that.
Futons can be a great alternative to a day bed. You can place them in the playroom, basement, office, practically anywhere. Some futons even come with storage under the seating. I love extra storage.
Renting a bed may sound odd, but if you only have guests sleep over a couple times a year this may be your best option. Check your local furniture and rental stores to see if they rent beds.
Murphy Beds can get expensive fast, but they are still cheaper than renovation your home. These are great options when floor space is at a premium, and you need a place to store your extra sleeping quarters.
I hope you have a great holiday season with tons of guests.