I've tried sandboarding on a variety of different common/easy to obtain items. Below are reviews of a few different items that I've tried or seen. If you have tried anything else and you think it's worth mentioning on this page, send me an email and I'll add it to the list below
Bodyboard 
Bodyboards go great down steep sanddunes, and you can either sit, lay or ride them dropknee - could probably standup too, but I haven't seent that.
There are a few things to keep in mind when using a bodyboard though;
Cardboard 
Cardboard is absolutely no good Whatsoever! for sandboarding on, there's always someone who shows up at the sand dune with a piece
of cardboard and expects it to work. IT DOESN'T, so don't bother trying.
For Sale Sign 
By far the best free sandboard you can have. Tie some rope on the front of it to hold it up as you slide toboggan style down the slope.
These things can really fly. I've also tried adding foot straps to the board with moderate success.... Mostly they're just best for tobogganing, so they're great for kids.
Tips for finding a good for sale sign;
Human Being 
Not a chance, unless you find a person and push them from the top of the dune and then laugh as they roll to the bottom.
MacGyver Sandboard 
I saw this on an episode of MacGyver called "The Gauntlet" where he supposedly makes a sandboard out of a map. Ok, this would not work... i'll just leave it at that.
Metal 
I tried a thin flexible piece of metal, and it didn't work, at all - actually it was probably lucky that it didn't cut my foot off or something, it was very sharp.
Plastic Tarp 
This will not work, a sandboard needs to be rigid.
Skateboard Deck 
This is actually half decent, I was using an old skateboard deck with some griptape on the top, which meant that it made it easy to stay on the board.
Because the deck is fairly small it was a bit difficult to balance, and I only really tried it on small steep dunes. But it was kind of fun.
Note: This will really wreck the bottom of the deck. After sandboarding, it looked like the bottom had been sanded. It was still usable, but if you have a pic on the bottom of your deck that you really like, I would not recommend
using it as a sandboard.
(Also this is only a good alternative sandboard if you happen to have old skateboard decks lying around you house :)
Skimboard 
I've tried a wooden Skimboard and it works okish. It isn't really bent up enough at the front to stop it form digging into the Dune, but it's worth a try if you happen to already own a skimboard.
Slalom 
While sandboarding we met Callam who was trying out a slalom down the dunes. He said that it's something that is normally used to tow people in behind boats. Anyway, it didn't really work very well in the
sanddunes cause the ridges on the bottom of it we're digging into the sand too much.
Snow Mat 
This is a thin peice of flexible plastic which is used to toboggan in the snow. It seems to work okish in the sand and was working best for lighter people.
Snowboard
I haven't tried sandboarding with a snowboard, so this is a review from Paul Stanley, who has tried it:
It was in the summer (well, I guess that's obvious) but I was really craving a run down a snow covered hill, but that was out of the question, so I did the next best thing, I took my board, went to the sand banks, (but I live in Canada, Trenton On, so I couldnt find a really big hill) but it was still great.
It was nice and fast, still carved, and we even made a pretty nice jump and got some picks and everything. all in all, I think it was very successful. the only thing is, if u snowboard, and have a very good snowboard,
DO NOT USE IT!! when u get going fast, its like taking sandpaper to your board, not a good idea. I regretfully did this, and my board was never the same, but luckily I got a new Ride 5150 that I keep on the snow, and an old Division board that I use for the sand.
Surfboard 
I tried an old foam surfboard (with the fins removed, of course) This didn't really work, but it did fit a whole heap of us on it... and uh, well it made it a few metres or so down a fairly steep drop,
and it was fun.
You might have more luck if you try a real surfboard ie not a foam one, but considering surfboards cost quite a bit, do this at your own risk!!
Waterski 
I tried an old wooden waterski that I bought at a second hand shop, it was really bad... I think it weighed too much. I ended up selling it back to the shop at a $5 loss.
Wood 
A plain plank of wood isn't going to work, you'd need to modify it a bit, This is a bit hard to rate as it depends on how you modify it, but the minimum modifications would be;