Panera has good food for a chain restaurant. I think their bagels and bread are generally delicious. Go for the Asiago Cheese Bagel with some veggie spread or cream cheese. Their Cinnamon Bagel is good if you're in the mood for something sweet.
I've tried the majority of their sandwiches but my favorites are the Asiago Roast Beef and the Frontega Chicken. They now have Mac and Cheese which is more flavorful than you'd think and worth a try, but I usually prefer their soups.
The biggest problem with Panera, and the reason they are only getting three stars from me, is that their sandwich portions can be ridiculously small. It's supposed to be a half sandwich but far too often it's like a quarter of a sandwich. Even with dainty bites you'll have it finished in about six bites. It's not bad for a light lunch but the price is a bit steep for what you get. The portions do seem to vary depending on who is making the sandwiches. I've had them range from nicely sized to ridiculously small. If they work to standardize these a little better it would be a big help.