DL: Don't miss the Indiana Jones Ride, it is amazing! I love DL Pirates of the Caribbean, and the Matterhorn is a DL exclusive worth trying. New Orleans Square is also really neat to wander around.
DCA: The Aladdin show is spectacular, get there early for good seats. Don't miss Soarin' (go early, and maybe even get a FP for later in the day), TOT is great, but different from WDW. California Screamin' is also really fun.
Downtown Disney is right outside the parks and full of shopping and great food. When I go to DL I usually leave the parks and go have lunch at DTD, just because I love the variety and the quality of the food there (food in the parks is great too, but DTD has been less crowded the times I have visited).
If you have more freetime in the L.A. area you may want to visit Santa Monica, there is a pier with a carnival style "amusement park", a nice shopping district (3rd Street Promenade), live entertainment, lots of restaurants and a beach (although, if you are looking for a beach day there are nicer beaches around). I always find Santa Monica to be a lot of fun, and its a nice break from the hustle and bustle fo L.A.