I've been pretty lucky in this area. Even though my TV is on ALL day (I know, some moms are probably shuddering right now LOL), my kids don't actually watch it all day. They watch their favorite shows and play, watch and play, and so on. They go back and forth all day. But there are some times that I just turn it off. When I do, they just find toys and play with them. I've been very lucky! Sometimes they even turn it off themselves.
I have been trying to make it a habit to turn off the TV when they eat lunch, when I sit them at the table to color, when we eat dinner, etc. We have a small house, so the TV is pretty close to the kitchen, but they can't see it from the table, just hear it. So I have been trying to get them in the habit of it being quiet during certain times.
Another thing you can try is turning off the TV and replacing it with a radio, or if you have kids songs, like those silly songs things, put that tape in. Then give them puzzles or coloring books to work on while they listen to the music.

If they really object, start off slow. Just ten minutes of coloring and the TV being off. When they ask for it to go back on, go ahead and let them have it. Remember, if yuo resist they will just want it more!
It's not perfect advice, but maybe it'll spark some ideas