TBS would be a good go to. They generally show sitcom reruns throughout the day. I used to miss a lot of school in high school and we didn't have expanded cable, so TBS was what took me through the day. I'm sure the schedule has changed, but when I watched it was Fresh Prince in the very early mornings, two hours of Home Improvement, and hour of Yes Dear, and then Everybody Loves Raymond.
I just looked up their midday lineup. Fresh Prince at noon, two episodes of American Dad, four episodes of Everybody Loves Raymond, and episode of Seinfeld, and then Friends until 6 PM, at which point you can probably start finding a variety of programming.
If you're into even older television shows, I'd imagine TV Land has some decent programming during the day.