I've been toying with the idea of using a mustard or onion poultice when I'm congested, but haven't gotten up the nerve to try it yet. I did try something new for this round of sickness though -- honey-onion cough syrup. Here's a link to the recipe and some general info about how much onions can help congestion.
It was easy to make...if you don't count the 15 minutes it took me to pry the lid off a new bucket of honey. Totally wiped out the little bit of energy I had.
I added a little ginger to mine and it tasted very good and felt nice on my throat. It seemed to ease the stuffiness a bit and reduce coughing. It gave me kickin' onion breath though.