The following resorts offer free skiing and riding for U.S. Military personnel with a valid ID:

Squaw Valley:
Complimentary lift tickets for active duty military members every Sunday through Friday, excluding holidays. To redeem, military can present proof of active duty status at Squaw’s Tickets, Passes and Snowsports Center at the base of the mountain.
Holiday blackout dates for the Military Lift Ticket program include: 12/17/11 – 1/01/12; 1/14/12 – 1/16/12; 2/18/12 – 2/25/12; and all Saturdays in the 2011-12 winter season.

Alpine Meadows:
Alpine offers active duty military FREE lift tickets Sunday-Friday, non-holiday, with valid Common Access Card. Blackout dates are December 17-31, 2011, January 14-15, 2012, and February 18-25, 2012.

Homewood Mountain Resort
Active duty military receive FREE lift tickets with a valid Common Access Card. Spouses and children of active duty military personnel also receive 50% off day lift tickets when accompanied by active duty military personnel with valid C.A.C. card.

These resorts offer discount tickets to active military:

Boreal:
$15 lift tickets on Fridays for all active military with a valid i.d.

Mount Rose:
$39 lift tickets when you present your Active Duty military ID at any Mt. Rose ticket window. Valid all season.

Kirkwood
Kirkwood is offering active duty military a FREE lift ticket on Sunday, January 22nd and Sunday February 26th , 2012.  Just show your military ID at the Season Pass Office in the Main Village Plaza to receive your free ticket.
Military tickets are available for $53 at the resort or from $39 when pre-purchased online.  You must show a valid military ID or a valid military dependent ID to redeem your ticket.  Online sales are available daily 12pm – 8am (not available 8am-12pm).