A hidden gem, but no longer around, was "Sky Chef." It had great Szechuan fare which I thought was more authentic than Laoszechuan. I greatly miss Sky Chef's Dan Dan Mian (noodles). I must say that I'm personally fond of LSC. Food is okay and staff is surly.
"Gourmet Food" on 23rd Street is a great inexpensive carry-out joint. It's definitely not a sit-down restaurant as it really is a shack. It offers good rice boxes at a reasonable price. 2 people can sometimes dine on 1 box which costs about $4-5. Lots of families buy dinner after work. College students on budgets are regulars. Classic home style dishes are their specialty, such as, poached chicken with ginger and onion sauce over rice, minced beef with peas and a fried egg over rice, salted fish & minced pork cake over rice, salt & pepper shrimp over rice, and on and on and on.
Ken Kee is a favorite of many Chinese locals. Lots of Cantonese and Hong Kong favorites.
Triple Crown on 22nd has cleaned up a bit and offers late-night specials of smaller dishes around $5/each. It's great after a night out. You can get several dishes and share with friends. Dishes are served with rice or a thin rice soup/porridge.
Ed's Potsticker House isn't really a hidden gem as it has received a lot of press but it does have great Northern Chinese breakfast on the weekends.
Grand Palace on 26th Street has been frequented by quite a few Chinese diners as I've noticed that their parking lot has been packed lately. But I've not dined there so I can't tell you what so many people are finding special there.
Happy dining!