Do you have little kids? Then hit Peter Pan right off, or Buzz Lightyear Astro Blasters. Its a blast, if you'll pardon the pun.
Don't? Then hit the new Space Mountain right off. It rules.
Hijos o hijas? I haven't been on the Monster's Inc ride, but I've heard its pretty fun. Soarin' Over California is really good. Depending on how much scares the little one, Grizzly River Run.
No hay de chiquitos? Tower of Terror is a MUST!!
Pero, de que a ver? The Aladdin Musical thingy is very good. We enjoyed it alot.
For Disneyland, I reccomend everything. Especially Indiana Jones, and Splash Mountain. Fastpass. Except Winnie the Pooh. *shudder* Also, Toontown is pretty hit and miss. The only thing I do there is Roger Rabbit.
DCA... well, the only things that we ever do are the Animation building, Tower or Terror, Soarin' Over California, Grizzly River Run, and California Screamin'. But whatever. You should try it all, because we're hard to please.
Sydney, Australia ... where there is no Magic Kingdom :(
Re: What should I go on?
I'd try and ride as much as I can, and it depends on how much long you are going to go for.
In my opinion, MUST RIDES include: Indiana Jones (I'd head there first); Splash Mountain; Space Mountain; Big Thunder Mountain Railroad, and depending on your tolerance level to sharp drops, the Tower of Terror at DCA and Soarin' Over California while you are therd.
Sadly, Pirates is closed at the moment, but Haunted Mansion is also a 'classic'.
To get that 'complete Disneyland experience', I also recommend taking the time to do a full circuit around the place via the Railroad or Monorail. The Railroad doesn't cut through DCA like the Monorail does, but you get to see the park at a more leisurely pace, as well as a few hidden surprises. Talk a stroll down Main Street, and hop on the Mark Twain Riverboat. The big rides are truly awesome - and worth the wait if there is one - but those little things just give you the full 'magical' experience.
“I don't mean to sound bitter, cold, or cruel, but I am, so that's how it comes out.” - Bill Hicks