You can never have too many pairs of wool socks.
A Thermos. There's nothing like a hot drink after a cold morning bike commute.
Hand cream and lip balm are winter essentials.
Nice panniers will bring style and convenience to your favorite cyclist.
A subscription to a bicycling magazine is a gift that keeps giving.
Fenders make commuting more pleasant.
You can also donate to the WI Bike Fed or Rails-to-Trails in the name of the cyclist on your list.