It is rare that coffee shops have amazing food and amazing drinks, but it's safe to say that Barriques has the best damn sandwiches in Madison. (and cookies and scones) The staff has always been helpful, and as someone who spends lots of time studying in coffee shops there is always ample room and a table or two free during the day. The WiFi has never disappointed me, Outlets are sometimes a problem as is cell phone reception.
The evening tends to boast a crowd out to have a good time instead of a good dissertation so stick to studying during the daylight hours.
I am a huge fan of the wall of 100 because after a day of staring at laptop I usually need a drink. (and ask for suggestions, if you have an idea of what you want they will be able to guide you)