This deal has ended.
Buy.com has the CamelBak HydroPak for only $19.99 plus free shipping and no sales tax (except CA, MA, MD, TN). These normally sell for around $30, before shipping and tax. Camelbak is the go-to for sports hydration: the HydroPak has a 50 oz. resorvoir (equivalent to two large water bottles) and an external zip pocket.