In my last short I used a hand-push golf cart (ala ), which has nice big wheels and is fairly dense --I was pretty proud of a few of the shots I managed to get ( especially because I was filming on tile). There are a number of ways a camera can be attached to one of these, but it probably isn't very useful for anything above really basic do-it-yourself films.
Just my 2 cents ;).
Tripods with wheels work nicely too...and escalators are great for "boom" shots :-p (though of course rather limited in their usefulness...)
