I can enthusiastically second the recommendation for La Folie -- a meal from chef Roland Passot's kitchen (especially when accompanied by wines selected by his brother, Georges) is my idea of heaven-on-earth. The decor is fun (sophisticated whimsy) and the staff is professional but not stuffy. The food is fabulous and it's plated with visual artistry. By all means, leave room for dessert.
Ristorante Bacco in Noe Valley (on Diamond Street) serves wonderfully authentic Italian cuisine in a relaxed, comfortable setting at reasonable prices. IMHO they serve much better Italian food than anyting you'll find in North Beach.
Of course, you can always dress up and head down to the Financial District for perfect cocktails, exquisite caviar, predictably excellent food and great live jazz at Bix -- another one of my favorites, with ambiance straight out of the Cole Porter era.
I'd better stop here before I start to salivate and ruin this keyboard . . . have fun!