It's a long day hike, but getting to Thousand Island Lake or to Garnet Lake would be nice. Actually for a day hike, the view of Garnet Lake is better.
Shadow Lake is an easier hike, and certainly would make a nice day.
Those hikes start from Agnew Meadows. You would either take the shuttle bus ($$) or leave really early (I think you can drive in if you go before 7 AM, but not sure.)
