YAY! Go West, young Screever....
Bengal BBQ is awfully swell. Jazz Kitchen was great at both lunch and dinner. Storyteller's Cafe was also good. Skip Cafe Orleans at breakfast -- powdered eggs! bleah -- but keep them on the to-do list for lunch. Make sure you have a corndog at least once from either the corndog wagon or the Corndog Castle in DCA; they're big, and they're awesome. Best corndog anywhere. Pacific Wharf Cafe in DCA has yummy soups and salads in fresh-baked sourdough bread boules, plus it's a fine spot to sit and peoplewatch and enjoy the day. Also at lunchtime, make sure you're in Frontierland so you can check out the show at the Golden Horseshoe.
Besides the not-at-WDW rides that other Buzzers already mentioned, I'd add a mention of the SunWheel (DCA). Make sure you ride it twice: once in the stationary gondolas (great time to take pics if the day is clear), and once in the rocking gondolas.
Oh, and Toy Storia Mania is supposed to open this year, woohoo! Should be in time for your arrival, too.
And like 6-2-6 said, the most significant difference is SIZE. DL/DCA will offer a much more intimate parkgoing experience, and it's easier to see the whole complex quickly and do all the things you want.