I lived in A-town from '86-'93, so my info is outdated, but - there used to be a great place called The Century Cafe. I checked online and it should still be at 546 N. 7th St. Was next to a lighting showroom. Their phone number is 610-821-0545. It was (I assume still is) a husband and wife owned operation, fairly small, maybe sits 50 with a u shaped bar on one side and seating on the other. At the time they had very inventive food for Allentown. I remember a flaming cheese appetizer that was out of this world.
Would also recommend The Sunset Grille. Great Mexican food, a little difficult to find if you're not from the area, but not too off the beaten track. They are located at 6751 Ruppsville Rd. 610-395-9622. Check out their menu at their web-site www.sunset-grille.com.
Based on my experience those would be my picks, but it's been awhile. Let us know what you find!
Anna in Philadelphia
The Century Cafe, sadly, closed a while ago, citing lack of patrons due to the unsafe neighborhood it found itself in.
If you're looking for eating places in Allentown proper, you may want to try The Mexicana Grill, at 407 7th Street. They have great Mexican food, pretty authentic. The owners are Mexican, and most of the family seems to pitch in at one point or another. Decor is nothing fancy, but comfy.
The Federal Grill is a very good place also, right on Hamilton Blvd., I think between 5th and 6th, or maybe 7th. Beware though, it is a cigar bar, but they do have an upstairs sitting area that is non-smoking. They serve excellent food at reasonable prices, though sometimes their experimental stuff can get a bit out there. Service can be slow at busy times. Excellent ambiance and decor.
I can't think of any others I'd definitely recommend in the downtown area, but you can visit Town Square, a site with Lehigh Valley listings that allows visitors to rate restaurants in the Eateries section.