I swear by mega-doses of timed-release Vitamin C and, more recently, wild oregano oil. The combination, taken for about a week, has for me reliably aborted colds and flu time if taken soon after the first telltale signs that "it's got me" have appeared. Wild oregano oil is not cheap (nor easy to find), but the expense pales in comparison to the cost of being out of commission for the better part of a week.
cough/cold/flu recipe
I would like to share my favorite remedy for the flu season. 1 quart chicken stock ( I buy it at Trader Joes), put on the stove to simmer with 8-10 cloves of chopped garlic. Add 1 tsp. tyme, 1-2tsp. of curry powder, a dash of red pepper, the juice of 1 lemon, and a handful of fresh mint. Let it simmer for 20-30 minutes. You can drink from a mug or bowl as much as you can take. Its great for opening up the nasal passages and is a wonderful anti-viral. My husband says it'll kill you or cure you! (the garlic) 
