Well, business appropriate is highly dependent on your particular industry. Cafe Agora is, bar none, the best value lunch in Buckhead. The service is quirky but the food is incredibly consistent and quite delicious (and trust me - i don't say that often). If you're looking for a more buttoned up affair, it's a lot harder to point you in the right direction. On the high end - bone's might be your best bet for the truly deep pockets. admittedly, i have not been there in over a year. If you don't want steak, but want something up there, the broiled (not boiled) lobster at The Palm is killer.
I have also checked out La Fourchette, only been there once, and for a more reasonable sum, i'd think there is potential there. Admittedly, i do not even recall if they are open for lunch. Henri's Bakery can put out some pretty good sandwiches, but don't get them out of the fridge ... have them make you one fresh. Annie's Thai Castle, while admittedly gentrified, is continually consistent and enjoyable.
Annie's Thai Castle
3195 Roswell Rd NE, Atlanta, GA 30305
61 Irby Ave NW, Atlanta, GA 30305
262 E Paces Ferry Rd NE, Atlanta, GA 30305
My vote for lunch has to go to Cafe at Pharr, although ironically they have moved out of the original Pharr Rd. location onto Peachtree. Also on Roswell Rd., in North Buckhead. My husband - who normally won't touch chicken salad - eats here all the time. I just love the yogurt rolls! Not exactly a hole in the wall, especially in the new location, but fantastic lunch option.