Maryland Day hiking ideas

I live right outside DC very close to the C&O Canal near the Billy Goat Trail.

Would anyone have any suggestions or lists for some good day hiking trails around me? I really like the Billy Goat Trail A section because of the view and all the rock hoping that one has to do. It's also just a little less than 2 miles so it doesn't take very long to get through.

I have a Garmin c550 so i can load some good starting points. I also have simple Magellan 100 which could help me find the exact start of the trail but i don't think i can load any trails because there is no base map.

Any ideas would be greatly appreciated.