Here's a deck someone built using wood pallets.

Sue

Here is a link that might be useful: Decking form pallets

I think this is a very good idea. I have two pallets I was considering ditching but now you've given me something to think about. Very clever.

Or perhaps use cinder blocks as your foundation? Or railroad ties?

We were in the same spot last year.
We did not want anything permanent, for real estate tax reasons, so we thought this would work.
We decided to use some recycled cedar fencing that we had.
We used some 4x4 posts, also recycled and made this floating deck.
Now if the assessor comes, we can tell her that it is not permanent!!

My friends just did this. They used plastic pallets though - they were concerned that wood ones would eventually rot. They sat the pallets on a bed of sand (where their above-ground pool used to be) and leveled them. Then they screwed regular decking lumber down to the pallets. The cut short pieces of lattice and attached them around the outside of the pallets so you can't see them - it looks like a regular deck with the lattice work hiding the support. It really did come out nice, although they did end up spending some bucks on the decking wood and lattice. But they want to add on to their house in a few years and the addition will probably go where the deck is now - this gives them the ability to move the deck when they need to.