Right by the Aquarium there are several agencies offering whale watching tours. We haven't been yet but it's supposed to be a ton of fun.
Retro Row on 4th Street has a ton of great restaurants, kitschy vintage shops, and our favorite movie theater, the Art Theatre of Long Beach.
If you have access to a car, there are some incredible cliffside views in nearby Rancho Palos Verdes. Places to check out include Point Vicente Lighthouse, Terranea Resort, and Founders Park.