We were planning on crusing Alaska on
DCL in May 2011, but after doing a bunch of research (especially here on Dis) we're going to cruise Princess in May 2011 instead and are now just waiting for the dates to be released. We plan to do a 7 day cruise and a 4-5 day land package. Princess seems to have awesome prices.

Good luck planning!
We cruised to Alaska on Princess this past August. We also did a 6 day land tour to Copper River/Denali/Anchorage. It took me 3 years to convince DH that we needed to go to Alaska so I did my research. Princess had the best itinerary (that worked for us regarding what we wanted to see) for the land tours so that was why we chose them. There were more elderly (70-80) than I thought there would be and the average age of the other cruisers was mid 60's about 10 years older than DH and I.
If you are doing the cruise or the land tour it is a good idea to research the different itineraries as to the ports of call, and the places on the land tour. Every land tour goes to Denali. You can take a 3, 4, 5, 6 or 7 day so where you go and what you see is up to you.
Not to be flippant, but once you see one glacier.......they are all pretty much the same. We went to Glacier Bay and College Fjord. But we talked to people on our ship and they had been to the Hubbard glacier and said it was beautiful. It's all beautiful.
This was a trip of a lifetime that I had been saving for. We got a balcony which was worth it's cost, plus stayed 3 extra days in Vancouver and 2 extra days is Seattle. I used frequent flyer miles for all the flights (4), and Hilton miles for our hotel in Seattle. I bought the Entertainment book for Vancouver and used meal discounts.
I also bought an Alaskan tour saver book that saved me 50% on a few of the excursions we booked our selves. We did flight seeing over the summit of Mt McKinley and I had a coupon for buy one get one free (from the Tour Book). Saved us $325. The book cost $99. So I made my money back and then some.
For the OP, the May and September cruises are much less expensive, but you run the risk of very cold weather.
I'm another fan of Cruise Critic. It was invaluable as far as information about the ship, the cruise line and the ports of call.
On the cruise we did one paid excursion per port and at all 3 ports had time to do sightseeing on our own. On the land tour we stayed at 4 different hotels over 6 days and did 2 excursions that we paid for. We had the Tundra Wilderness Tour that was included in our tour package. If you take a land tour.....make sure you do this at Denali. HAL often includes the Natural History tour. We didn't take that tour but people on CC stated that the Tundra Tour was much better. The days we didn't have planned excursions we explored on our own. There was always a LOT to do.
Be aware that if you do any kind of land tour, few meals are included in your package. You must pay for them yourself. Copper River was in the middle of nowhere so our only choice was to eat at the hotel. Thanks goodness the food was decent.
HAL and RCL use Princess Hotels in Denali. They do have their own bus/rail system but Princess owns the hotels.
Send for brochures from the towns in Alaska you may be visiting. Plus Alaska dept of tourism. They have great info and it's free.
If I think of anything else.....I will post.