One of the most concerning things about going vegan for me was giving up going out to eat, one of my favorite things to do. It has been a challenge, but while Frederick is certainly not the most vegan-friendly town to go out in, it also isn't the worst. Here are some of my favorites:
Cafe Nola-Look, just about every restaurant has something vegan to eat even if it's only a salad, hold the meat and cheese. What sets a place apart for me is whether it actually creates dishes that are interesting and delicious specifically for vegans. Nola always has a few great options that don't sacrifice anything to be vegan. The pace is pretty laid back there, so if you're in a hurry you might want to go somewhere else, but if I want to take some time to enjoy a great meal I usually head to Nola.
The Orchard-A close second. Food is great, but the options are a little more limited, pretty much only soups and stir-fries are vegan. But again, I really appreciate a place that creates dishes specifically for vegans.
Bangkok Thai Kitchen-the menu doesn't look very vegan friendly, but they will make most anything with tofu and veggies instead of meat, and the food is great.
Not in Frederick, but worth the trip, Great Sage in Clarksville--there's no meat on the menu at all, and just about everything is vegan or can be made that way. Only been to brunch and lunch there, but I look forward to going back and trying more meals there. It's neither hippy-dippy nor pretentious, just a great restaurant that happens to be all vegetarian.
That's about all for places that actually cater to vegans, but there are good options at other places:
Romanos Macaroni Grill-I worked there, so I know the menu pretty well. Beware! The tomato-basil sauce is made with meat stock. The arrabbiata (spicy tomato) is vegan, though, so you can create your own pasta with that and veggies, or do olive oil and garlic. They saute everything in butter, so request no butter. Best of all, the rosemary foccacia is vegan.
Hard Times Cafe-I have read the vegetarian chili is vegan.
Baja Fresh-Not in Frederick, but I work in Rockville so I go there for lunch. You can do the grilled veggie burrito with no cheese or sour cream. Both the pinto and black beans are vegan, as are the tortillas. Take your receipt and do the survey online and you can get a free pronto guacamole next time you go.
As I write this, I realize I haven't been to too many restaurants since I went vegan, so I guess I'll have to update this as I get more info. If anybody happens to stumble across this and wants to share your their opinions and experiences, please do!
Btw, I should mention that I've gotten my data on what's vegan from various sources, and while I believe it is reliable, I can't make any guarantees. If you have any concerns about my accuracy I urge you to verify it for yourself.