It's been a while since I've been there, but the Charleston's on NW Expressway always seemed to have a pleasant atmosphere, as does Bravo at Memorial and Penn. Both are regional chains.

Locally, you might try the Paseo Grill (depends on your budget). They have lots of neat curtained off areas and intimate spaces perfect for good conversation.

I haven't been there at night, but 1492 - at least for lunch - seems like it wouldn't be a bad spot.

La Baguette is also a perennial favorite, although it can get a bit cramped at its busiest times.

Some really high-end places I can think of that have that type of atmosphere are the Boulevard Steak House and Mahogany.