I love Octagon Cafe for lunch. It has been nice to watch it develop over the years. I always get the turkey and avocado sandwich with the lunie birdie salad (a awesome take on Waldorf with candied pecans and AMAZING chicken salad on top). Their salad is one of their strong points (don't get me wrong their sandwiches are great too, but I actually crave the salad). Another big win for them is the iced tea. I am a huge iced tea person. They have this apricot mango tea (unsweetened) that is just awesome.
Octagon is a great place for lunch conversation with its relaxed quiet atmosphere. You can sit on the patio if you'd like to watch the Fountain as it goes off.
Also, once you are done, if you are still hungry, they have great frozen yogurt (not on the menu) and you can add toppings to it. I like to get swirl with Oreo and the candied pecans. Talk about yum!