I'll second Riccardo Trattoria for semi-upscale Italian. Chicago Pizza & Oven Grinder is great for a casual place, but there may be a wait to get in. For another casual place, have you thought about R. J. Grunts - the original Lettuce Entertain You restaurant?
Another thought - right next door is possibly the most romantic restaurant in the city - Geja's. Fondue accompanied by flamenco guitar.
I've also heard that Zia's, which is basically on top of Geja's, is good for Mexican/Southwestern, plus it's BYOB. But I haven't tried it personally.
Riccardo Trattoria
2119 N. Clark, Chicago
Chicago Pizza and Oven Grinder Co.
2121 N. Clark St.
R. J. Grunts
2056 N. Lincoln Park West
Geja's Cafe
340 W. Armitage Ave
Zia's
340 W. Armitage Ave.