For those not wanting to DIY, the elderberry concoction in the stores is under the brand name of Sambucol (and it works great)
My family began taking starting October, weekly, a vial of homeopathic Oscillococonum to stave off colds - and we've yet to be felled by one this year. By now each Winter we would've been been tanked by one or more already.
Good stuff - rediculous as it may sound - it's incredibly small dosing of goose or duck liver it turns out to be. Good stuff!