Footprints are definitely a bit unnecessary. Tent floors are made to be puncture resistant and waterproof (or at least highly water resistant). The only reason to use a footprint, in my opinion, is if you want to ditch the inner tent and just pitch the fly.

I've used painters drop cloth, the 2 mil plastic variety, cut to size, and it works, but it lacks durability. In about a week, it's so full of holes that it needs to be replaced.

Tyvek housewrap works well; it's light and durable, but it can be a bit loud, and it doesn't pack all to well. It's still cheap and works well.

I've heard really good things about Polycryo, the stuff used to insulate windows. It's supposed to be lighter and more durable than even Tyvek.

I'm not a fan of the blue tarp stuff; while it's really durable, it's far heavier than it needs to be. Unless you're camping on a bed of nails, you don't need a floor that bombproof.