OK, here is a list of places I have been to and a short description:
Cafe Express -1422 W Gray, It is a Sandwich and Salad spot. Pretty nice and if you go during the early evening, it is really cool as it has a view of Main. Not really a place to take someone to impress someone, but I like it because it is really laid back and has tables out on the sidewalk. I great place to start an evening.
Downtown Aquarium - 410 Bagby St. Really fancy. Very pricey but probably the most impressive restaurant in the city. Food is so-so, but again you are going for the atmosphere more than anything. This definitely fits in the fancy category.
Mingalone Italian Bar & Grill - 540 Texas Ave Bayou Place. Cool place, I just hit the place for drinks one night, but I have heard the food is really good, yet the service is hit or miss which can result in your food being warm instead of hot when it gets to you. I would think if you go on a night there is no opera, the service should be fine.
Saba Blue Water Cafe - 416 Main. I have had a great time everytime I have gone there. It is seafood, but the service is great. the place is never packed, so it is a quiet place with a nice, clean design.
Sake Lounge - 500 Texas Ave Bayou Place. Sushi joint, very classy. Priced right and pretty much in walking distance of everything. Very good service too.
Those are just the places I have been too. Hopefully this helps.