Here is an absolutely beautiful hike that I'm sure is great all summer but spectacular in the Autumn! It may be a bit late now but if you can get up to Moraine Lake when the colours are full, it is a wonderful hike.
I suggest going during the week if at all possible. From what I have heard the parking is next to impossible on the weekends. Even so, we got there on a Tuesday afternoon about 1 - 1:30 and the parking lot was full. It was emptying out though. We were pretty close to the last people going up. Take note though that there is a sign at the beginning of the trail warning you that you will be fined for groups less than four. We were fortunate that there was another couple waiting for 'us' and as their pace was close enough to ours it made for a pleasant and safe hike.
It is a pretty steady uphill hike - I think about 750 feet up from the Lake. The work was so worth it though. We were not but if you have the time and energy, there is a trail up the gravel to Sentinel Pass.