This map identifies several businesses that rent bicycles in the Washington, DC area. Rental locations are shown in proximity to major multi-use trails (in red). Daily rental rates are shown on the right. Keep in mind that most locations also offer half-day and multi-day rates. Bike and Roll also offers several guided bicycle tours of downtown.
Also, don't forget about Capital Bikeshare (CaBi). For only $7 per day, you can check out a bike as many times as you like from over 300 self-serve kiosks around town. Additional fees apply if you checkout a bike fore longer than 30-minutes at a time.