You're going to love Alaska! But I cannot stress this enough: If you are traveling all that way and spending all that money--spend some actual time IN Alaska!! You don't need to sign up for the expensive Cruisetour--it's way cheaper and just as fun to go it alone!
We did the Celebrity Millennium northbound last summer, Vancouver to Seward.
This was our itinerary. We flew to Seattle and spent the night (if you can swing two nights, do it, it's a fabulous city!). Next morning we hopped an Amtrak train to Vancouver. We did need passports, but border crossing on the train couldn't have been simpler. Arrived in plenty of time to board the ship.
In Skagway, we took a free historic walking tour from the National Park Service and saw the "Days of '98 Show with Soapy Smith." In Juneau, we did a bus tour that included Mendenhall Glacier (nice flat walkway to Photo Point, very close to the glacier). We also stopped in Icy Strait Point, which is a tourist spot with beautiful easy hiking trails, a rocky beach where we stuck our hands in the freezing water, and a nice fishing museum. The best was Ketchikan though. Have you seen Deadliest Catch? There's a Bering Sea Crab Fisherman's Tour on the Aleutian Ballad, the boat that took a rogue wave on camera in Season 2. All the tour guides are former Bering Sea crab fishermen, and they show you all the equipment and tell stories of their adventures. We also cruised past the Hubbard Glacier.
Is anybody in your group a veteran? We got a fantastic military rate last year, good for anyone with 2 years service and an honorable discharge. We paid just $299 per person for an inside cabin! I agree with the poster above who said you really don't need more than that. We were only in the room to sleep and shower, otherwise we were out on deck. Celebrity's a wonderful line for all ages...we usually prefer Carnival, but this was just slightly upgraded without being snooty or boring.
When the ship docked in Seward, most people immediately hopped a train for Anchorage and flew home the same day!

We stayed in Seward for over a week, then spent two more weeks in Anchorage. We meant to get further into interior Alaska, but we were having too much fun where we were. We're driving back with our RV next summer though, so we knew it wasn't a once in a lifetime trip.
Even if you can only squeeze out a few days, do it. The Seward to Anchorage train is one of the most scenic in the world, and interior Alaska is so different from the port towns.
The single best piece of advice I can give you: Buy the
Great Alaskan TourSaver. It's $100 by mail order (also sold a couple of places in Alaska) and it saved us literally thousands. The book's full of 2 for 1 deals on everything from train tours to hotels to RV rentals to tourist attractions. Just plan on one for every two people in your group, because the coupon has to be attached to the book when you present it--so you can't tear out two coupons and give them to different parties that are splitting off. Seriously worthwhile though.
Here's the
first in an article series I wrote about our cruise--hope you find something worthwhile in there!