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 $5 per day, you can rent bikes as many times as you like for 30-minutes or less. You pick-up and drop-off the bikes from over 110 self serve kiosks around town. Additional fees apply if you need to rent for more than 30-minutes.