Kristin's passed along some cold season tips I've never heard before (and wish I had years ago):
These are all from our pediatrician, and have helped lower the number and severity of colds that the kids get.
Immediately wipe down their faces (especially under the nose) and hands whenever you put kids back into their car seats. Helps keep the cold critters from staking a claim. We use diaper wipes.
Don't let them nap in the clothes they wore outside. Better yet, remove all clothes after play in communal areas (parks, indoor playgrounds, PRESCHOOL) and toss them in the laundry. We nap the kids in their PJs.
Spray saline solution into their noses every night. Target sells small bottles for about 79 cents and they last a month or so. Be sure keep your squeeze on as long as the tip is in the nose (to not suck in snot), then spray a bit out into the tub or sink after you've sprayed in the nose (to clean the tip).