Campisi's in downtown is a great large group location. We used them a few years back for our rehearsal dinner and they did a great job accommodating a group of about 50.
For a smaller group, check out Cane Rosso in Deep Ellum. Easily the best pizza in Dallas and they are my favorite "everyday" place to dine in town for the laid back atmosphere, excellent pies with fresh ingredients, and selection of microbrews. Monday nights are also "guest chef nights" where they bring in notable chefs at other top restaurants in the area (Dean Fearing, John Tesar, and Kent Rathbun to name a few) and let them man the pizza oven for the night.