Our daycare's policy is that the kid can't come in (or is sent home) if they have a fever, vomiting, or diarrhea. They have to be fever/vomiting/diarrhea-free for 24 hours in order to return.
I agree with others that keeping a kid home for a runny nose w/o fever just isn't realistic--they'd be home every day in the winter! Their noses get stuffy from indoor heat, which dries the air, and the stuffy nose from a cold can last a long time. I keep my baby home if she's got a fever, but when the fever is gone and she's energetic and happy and feeling fine, but her nose is still stuffy, I'm not keeping her home. I don't go by a single symptom--if she was stuffy AND lethargic or cranky and not feeling well, I'd keep her home.