I really like the Polar insulated water bottles. Load with ice, fill with water, and it'll keep the water chilled for 90-120 minutes (my commute is only 40-50 minutes).

Camelback makes insulated bottles too, but I prefer the Polar because (1) I actually like the loops to hook over a finger as I carry panniers into my work (or out to the garage in the morning; (2) I prefer the traditional cap closure to the Camelback squeeze -- ever grab a bottle around the middle and dribble water over your panniers down the hallway?; and (3) the Polar closure is more reliable, IME, on bumpy roads and bike parts -- vs. water bouncing onto my legs.