Gray Line tour of Portage Lake, south of Anchorage (map). From what I'm told, Portage Glacier is relatively small, as glaciers come. It looked big enough to me though. The deep shades of blue that were buried in the crevasses were amazing, even from a few hundred feet away. Overall the tour took about an hour. The tour is operated by a private company, but a Forest Service employee gives an excellent narration throughout the tour. It was a nice little side trip before I had to depart Alaska. I'd recommend it if you only have a little extra time in Anchorage.