The Alaska Pass (206/463-6777 or 800/248-7598, www.alaskapass.com [1]) is a good option if you plan to travel using a combination of ferries, trains, and buses. Passes are available for varying lengths of time, and you can either buy one that allows travel every day (not a good idea if you want to do something more than sit on a bus or ferry) or one that lets you travel a certain number of days out of the total. The latter cost $799 adults or $400 kids for a 12-day pass that includes 8 travel days; or $979 adults or $475 kids for a 21-day pass that includes 12 travel days.
Links:
[1] http://www.alaskapass.com