Don't live there now, but a native of the area...I think that counts...so I'll chime in.
Most small coastal towns are nice. They are also expensive. That would mean San Clemente and San Juan Capistrano to the south and Oxnard Shores and Ventura to the north. Personally, I loved the maritime layer that shrouds these towns in a cool gray mist in the morning, that then burns off.
Slightly bigger towns would be Hermosa Beach and Manhattan Beach. They still have a sense of community. San Pedro can be hit or miss...proximity to the port and all the ocean liners coming and going would make me a pig in $h!, and there are some nice areas as you go up the hill, and some crappy areas near Gaffey that are very "ghetto." Also worth mentioning are Redondo Beach (particularly Hollwyood Riviera, nowhere near Hollywood itself), Huntington Beach and Seal Beach.
Long Beach is too big of a town, at almost 500,000 people. Venice is too bohemian. And Santa Monica just plain bothers me and is waaaay overrated. It's kind of soulless, with it's numbered grid and bland shopping areas that haven't been updated.
Inland, there are few towns of note. The whole south side of the San Fernando Valley has an "ok" individual community feel while still being counted within LA's 4 million residents. I have always liked Calabasas, Woodland Hills and Sherman Oaks. There are some interesting mountain communities perched up in the foothills of the San Gabriels and San Bernardinos, such as Montrose/Tujunga, though tough for commuting into the city's core or the West Side. In reality, they are better for Pasadena or SGV workers. Incidentally, I do not like anywhere in northeast Los Angeles metro, and think Pasadena is also overrated. It looks butt ugly when the San Gabriels are so damn parched in the summer. The only SGV community I like is San Dimas, for its hilly topography and reasonably nice residential housing stock.
Hope that helps. I know croc and tmp are also valuable resources when it comes to this topic. The O.C. might be a little too biased. :wink: