DC Metro Transit - Free This free app gives real-time predictions for the DC Metrorail, Metro Bus, Circulator, PG County - The Bus, Fairfax CUE, and the UMD Shuttle. I's ad-supported and tablet friendly - has trip planners, an interactive map of the Metro rail, will map you to the nearest station, and tons more. Basically the best app for DC public transport info.

Washington Area Metrorail This app sorts the DC Metrorail into stations - and allows you to see the "next train" info for any station in the system. You can also sort by line or by distance from your current location and you can mark favorites. Only for the metrorail.

Washington DC WMATA Bus Finder This app sorts the WMATA bus line into stops, and then gives you the real-time arrival info for buses at that stop. It costs $2.50. Crashes frequently, but when it works it's very accurate.

DC Metro Rails Real time train arrivals and alerts for the DC Metro. You can favorite stations and make shortcuts to them on your home screen - which is a very nice feature. Fast search results.

DC Metro Arrival Times This app is the fastest way to search for the next train's arrival time at a given station in Washington DC. Very quick results and easy to use. Simple.