Earlier I wrote about Columbia Heights Day coming in August, and a few commenters and tipsters have emailed me about Fiesta DC as well - it's DC's Latino festival, and it'll be on 14th Street in Columbia Heights on September 27th. The website shows bands, food, dancing, and other cultural activities. They don't have too much information yet, but it should be pretty cool -- and it makes sense to have it here, as CH, Mt. Pleasant and Adams Morgan (to a lesser extent) are the center of Latino culuture in DC.
I'm guessing it'll be around the Columbia Heights Civic Plaza, but not sure yet.
It seems like Columbia Heights is a main spot for festivals lately - there was the Caribbean Fest this weekend, Columbia Heights Day, and now Fiesta DC.