I agree, go to Seward. I've been several times, and I'm going next weekend!

I highly recommend the fjord tour - they have several different itineraries available, but you will get to see the glaciers up close, and quite possibly some whales. Use this link and go down to "day cruises."

The beginning of September is when the weather starts to change - it could be beautiful, or it could be cold and rainy. I recommend a raincoat and dressing in layers.

You still might be able to do some Silver Salmon fishing at that time, if that interests you. Many charters operate out of Seward.