What not to miss....
In DL my DNM rides are Indy, Matterhorn, Roger Rabbit, POTC (better than the WDW version), IASW (also better at DL). Also be sure to do the dark rides they don't have at WDW... Alice in Wonderland, Mr. Toad, Pinnochio (sp?).
At DCA you can't miss Soarin' over California. This has to be one of the absolute best Disney experiences. Grizzly River Run is a really fun raft ride, similiar to Kali at AK, but many feel it is better and longer (and you will get wet!). If you like coasters you will want to ride California Screamin'. Nice coaster with a very smooth ride. Also check out the Animation Building. The new ToT might be open by the time you get there as well.
As for shows, don't miss the Fireworks (Believe, There's Magic in the Stars). It's probably one of the best Disney Fireworks shows running. Also, in DCA, you will want to check out the Disney Electric Parade. This is a classic and a lot of fun.
For food, whatever you do, you need to be sure and make a PS for Blue Bayou. The food is good and the atmosphere is great. The restaurant is built as part of POTC and you get to watch the boats drift by after they leave the loading dock on their way to the first drop.
That's all I can think of right now, but there is so much more to see and do. Hopefully some others will add to this thread.