Rollerblading, Skating, Skateboarding
Rollerblading is most fun in Venice, Santa Monica, Hermosa Beach, and Huntington Beach-Newport Beach.
(Venice is called the "Skating Capital of the World", and Santa Monica is next to it)
"The Strand" is a path used for Skating from Redondo Beach thru Hermosa Beach, Manhattan Beach, Playa Del Rey, Marina Del Rey and Venice to Santa Monica.
Skating is also fun in Long Beach from Shoreline Village to Belmont Shore.
In Orange County, from Bolsa Chica Beach (at the north of Huntington Beach) to Balboa, the south end of Newport Beach's Boardwalk along the beach, is about 30 miles of bike paths that double for skating.
Seal Beach has skating, too, but it doesn't connect to BelmontShore/Long Beach or Huntington Beach directly, except by PCH (Pacific Coast Highway).
The Athletic Singles Association is a great place to bike or skate your way to meeting others of like mind in LA, Orange County, or San Diego.