Disneyland... a day, easy. Universal... same thing. You could also look at Knott's Berry Farms or Legoland, too. Just bring you wallet... and a friend's too.
LA is certainly huge, but it's not everything. When you're in LA you're 90 minutes from Santa Barbara, which is beautiful coastline farther north. You can also drive the PCH, the Pacific Coast Highway, to see what you can see.
You can sit in on the taping of a TV show (get your tickets in advance, though, I think).
Rodeo Drive. Hollywood. The walk of fame. Venice Beach (keep an eye on your wife there
). Tons o' stuff... limited only by your imagination.