Here are some national chains that provide free Wi-Fi access in some or all of their stores:
All Apple retail stores. See www.apple.com/retail/ for locations.
Panera Bread is aiming to have all their locations offer free Wi-Fi. In the meantime, many Panera stores already are "unwired." See www.panera.com/wifi.aspx for details.
Many Schlotzsky's Deli locations. See www.schlotzskys.com/wireless.html for a list.
Here are a few of the national chains that provide Wi-Fi access in some or all of their stores using a paid provider (this means that you have to pay for your access):
Barnes & Noble stores rely on different providers, including SurfHere. The best way to find a Barnes & Noble location that provides Wi-Fi access is to use one of the directories listed in the section "Online Directories."
Borders bookstores are "unwired" using T-Mobile Hotspot's network. The best way to find a Borders location that provides Wi-Fi access is to use one of the directories listed in the section "Online Directories."
Some McDonald's locations are being equipped with Wi-Fi access. The providers vary depending on the location (in many stores, it is SurfHere). See www.mcdwireless.com/ for more information.
Starbucks. Wi-Fi access is provided by T-Mobile Hotspot. See www.starbucks.com/retail/wireless.asp for locations with this service.
Many of the UPS Store branches provide Wi-Fi access using SurfHere or other network providers. Check with a local store, or use a Wi-Fi directory, to see if Wi-Fi is provided in a specific location.