It's tough to choose only four, but here goes my picks:
Tru - this is the big splurge, but its an experience to remember. They do degustations here so you can choose from a 4 course meal to a grand 13 course feast. Each course is fascinating and fun. Very sleek dining room.
Frontera Grill - not exactly downtown, but close enough. This chef, Rich Bayless, is nationally known for his excellent authentic mexican food. Fun, casual restaurant. Savory food.
Shaw's Crab house - pristine seafood, clubby environment
Spiaggia - another splurge but great great upscale italian.