I am a student who will be traveling to Alaska in a few weeks for just under a week. I know it's not much time - please spare me the 'you have to stay longer than that to see anything' lines.
For those who have some experience travelling in Alaska - what are the must see things for a short trip? The way I see it, I can either fly into Anchorage and do the Kenai Peninsula and Denali or fly into Juneau and do the Inner Passage stuff (glaciers, whales, railroad). Any thoughts on which is better suited? Cost is somewhat of an issue, and I'm curious if a few ferries around the inner passage (JNU) is cheaper than a weeklong car rental (ANC).
Thanks for any advice.

I can't tell you anything about the inside passage but I have a strong suggestion if you choose the Anchorage area. Pick either Denali or the Kenai Peninsula but don't try and do both in just five days. That is too little time to do either justice when you do both.

My personal preference would be the Kenai but I'm not you. If it were my trip, I'd head down to Seward for two days then to Homer for three. In Seward, I'd be sure to take one of the long glacier cruises-you'll likely see more sealife and wildlife than on the shorter cruises. If you do a board search on Homer and on Seward, you'll find lots of information on things to do.

Have a great rip.

It'll take you 3 days just to do Denali--5 hours up, 8 hour bus ride next day, 5 hours just back to Anchorage. It's another 2-3 hours down to Seward, much longer over to Homer.

Pick one area.

If you are interested in Juneau/Inside Passage, you can do a couple of things in this short time. From Juneau, you can go to Tracy Arm for glacier viewing or you can go whale watching. I suggest Adventure Bound for Tracy Arm and Orca Enterprises for whale watching. The fast ferry (M/V Fairweather) now runs to Skagway rather quickly (leave Juneau 12:30 p.m. and arrive in Skagway at 3:00 p.m. I saw it while I was up there in May and it's a beautiful boat. You could spend the night in Skagway, do the train the next day and then take the ferry back to Juneau. In season, there is also a fast ferry from Skagway to Haines if you want to take a quick trip over there (check the schedule though so as not to miss the other ferry). The fast ferry also services Sitka from Juneau, but only on Weds. & Sunday (check AMHS schedule to be certain). I just did Sitka and Juneau in in 5 days, so it is possible to enjoy AK for just a few days if that's all the time you have. Have a great trip.

I haven't been to Denali, only north of Anchorage as far as Trapper Creek. It's a loooong drive between Wasilla and Talkeetna and then further north. I think you will see more if you head south. Assuming you don't arrive too late in the evening and you aren't tired, it might be possible to head right down to Seward and take the longest glacier viewing cruise you can the next day. We were served a choice of fried halibut or chicken fingers lunch on our trip. Simple but sufficient. The next day, visit the Sea Life Center and explore the town. We missed the earthquake film that is shown by a local group. Head to the natural foods store (Yolies?) for sandwiches etc for a budget supper. I would also base which to do first, Homer or Seward, on 1)the weather, 2)when the farmers market is open (Sat 10-2 in Homer) and/or 3) where Hobo Jim, Alaska's balladeer, is playing. (Seward on Sundays, Soldotna at BJ's bar on Thurs etc.) Take the opportunity to talk with the tradespeople at the farmers market and get some goodies for breakfast. Best food for the money in Kenai is Ski-Mos across from the visitors center which has a great art exhibit. Depending on traffic it's about another 1.5 hours to Homer. The Pratt Museum is great. Take time to view each of the short videos on life in Alaska. Enjoy the funky places on the Spit. Take the scenic drive up the mountain to overlook the airport and town. A half hour flight-see with Smokey Bay Air is about $45. On the way back to Anchorage, stop at Portage Glacier Visitors Center. The movie cost $1.
We have taken the ferry up the Inside Passage but only got off at Skagway. You will probably see whales on the trip but for calving glaciers the day cruise from Seward might be the best. We did not see any calving glaciers on the ferry trip. Out of Seward the boat will stop for 1/2 hour, turn the engines off and let you watch and listen. If you are staying at a B&B, check to see if you are getting a home-cooked breakfast or simply a muffin and OJ. You might not care or you might find a big breakfast will let you get by on two big meals a day. Also check the schedule of events in the towns you visit for free events or something you're interested in. Larger events are listed on the Anchorage Daily News website. Hope you have a great time!