I like a boat ride--especially when it's cheap, or better yet, free. Apparently I am not alone. When word spreads about a boat ride deal, just watch the people come!  Among the cheap rides offered year-round, there's a decent, short Balboa Ferry which costs about $1. Bring on your car and another dollar to your fee. Most just like to walk on board but you can bring bicycles and pets.

Starting up on Memorial Weekend in Long Beach the colorful (red, purple and yellow) Aqualink high speed catamaran begins its summer routine traversing the Long Beach coast. It's not free but for what you get it's worth the $5 fee one way. Long Beach Transit also operates a small water. It only costs around $1. In addition there's a free Passport Bus. 

In Marina Del Rey the Water Bus opens some time in June and stays open through early September. Fee is around $1.

San Diego has the Coronado Ferry, and San Francisco is supposed to have a new water taxi shuttle service, but you'll find several commuter ferries between the city and East Bay.

In Santa Barbara the Water Taxi called Lil' Toot operates every 30 minutes during daylight hours. Fee is around $4, $1 child