What kind of screws are used for plywood subflooring?
It should be noted that the above linked screw is a sheetrock screw, not a subfloor or underlayment screw, which you will probably find in real life labeled something like "deck screw" if you're working on the cheap.

Sheetrock screws are brittle and prone to breaking under the flexing/shifting of a floor. DO NOT USE sheetrock screws.

My apologies to the OP for not viewing this page 18 months earlier.

If you're installing tile, or doing anything involving concrete (like self leveler), you'll want to look into screws that are alkali resistant. The cement board that you'll grout to the latex primered (better bonding, moisture barrier) subfloor will also be attached with these screws, and the fiberglass tape you'll use to "mud" the seams between the cement board (just like installing drywall) will also be of an alkali resistant variety. In both cases of subflooring and cement board, leave a 1/16" gap between sheets for building shift/expansion.

One final note, if you're adding plywood subflooring over an existing subfloor, screw the original sub to the joists anywhere it's loose, and screw the new sub to the old sub but NOT to the joists. This will help the floor float during the inevitable expansion and contraction of temperature and humidity swings.