A lot of the better restaurants in Gaithersburg are in pretty crappy locations (strip malls). The Nibbler is probably one of my favorites for a good cheap eat. Its not pretty inside nor is it very large, but the food is pretty good for the price and the employees are friendly. I have had the Lomo Saltado and the Ropa Vieja, both of which I think are pretty good.
Fu Shing Cafe is pretty good for Chinese and its behind the shopping center that has Borders, Ross, etc. I havent been there over a year so I cant speak for the quality now.
I have always thought Old Siam in Olde Towne was pretty good but its always empty. Junior's Chicken in Olde Towne is decent but I prefer Crisp and Juicy. Brooklyn Deli in Travilah Shopping Center is not bad either. The pastrami I got was a bit too fatty and I think I preferred the deli that was there before.
The other places that have been mentioned, I would agree that they are decent but nothing special(Tandoori Nights, Moby, Ay Jalisco, Momo Taro).