Mud flaps

Mud flaps are nice because they catch road spray down low, but won't catch air like a parachute. If there is enough clearance between your pedaling feet and the front wheel, you could add these to your front fender to protect your feet and the bike's chain and gears. And if you pull a trailer or buddies ever ride behind you, then you (or your buddies) will appreciate a mud flap on the back of your rear fender.

See bike nashbar for a good selection of ready-to-use flaps.

You can also create custom truck-style mud flaps using the instructions here and here.