San Diego. Beautiful place and tons of character. Sea World and the zoo there are amazing.

Definitely, absolutely, positively Disneyland! They don't call it the happiest place on Earth for nothin! If you can stay at one of the resort hotels fantastic - get to have a bit of a rest in the afternoon if you're shattered - you WILL be shattered but oh so much fun - and also cuts down on travel time. You can also buy special entrance tickets where you can get into the park I think up to 1.5 hours earlier than the general public on specific days of the week. Might not sound like much, but when you can queue for one ride for that long, the benefit of going without the crowds is huge. Also try to purchase the fast track (I think that's what they're called) tickets so you can jump to the head of the queue.

San Francisco is amazing. Also driving up through Oregon, Washington State etc to Seattle is absolutely stunning but depending on your kids, the beauty of the drive could be outweighed by their boredom.

Vegas is one of those must see places but for me it wasn't a highlight. Grand Canyon is worth a trip to the States all by itself.