We watch TV for entertainment purposes and I do limit it, because it has highly addictive properties for my children. I notice that they complain when I turn it off. And I notice that, when the TV/VCR/DVR has been off for a day, the kids play more cooperatively and creatively. So, I'm fine with them watching it, but I do limit the duration each day.
Even though I consider it an entertainment vehicle, some shows have educational value to me.
"Between the Lions" on PBS helped my oldest when he was initially learning to read. He didn't want any direction or help from us, but he was happy to watch the show and work things out himself. I could walk by and hear him sounding words out.
They LOVE the Zula Patrol on PBS, which is a cute little cartoon that talks about science concepts. My 5 year old learned about photons on that show.
They also love Reading Rainbow, although I have to screen it for adult content (e.g. Nazis, 9/11, etc). It mostly introduces them to new ideas and places. They recently watched an episode about mummies, in which scientists scanned mummies and built models of skulls. My oldest really took to that. They've learned about animals, like manatees and bird rescue/rehabilitation. There was an episode based on ds2's favorite book, "Zin Zin zin, a violin!" in which they visit Julliard to see the orchestra. My oldest is very artistic and so he really loved an episode about recycling in which an artist makes things from old appliances. I find a great deal of educational value in Reading Rainbow, although I put it on for entertainment.
They also like a show called, "Fetch with Ruf Rufman" on PBS, in which teams of kids perform science challenges. The episode in which they go to Kennedy Space Center was really popular at my house. Heck, I learned that newspaper is an excellent insulator from the lemonade stand episode. They also like Mr Rogers, when he tours factories. My husband tapes, "How it's Made" for my oldest, because he likes stuff like that.
Mostly, I've found TV to be valuable in bringing my kids to places they've never been before and showing them things they've never seen before, kind of like a book. You can get fabulous books about mummies. But you can actually watch a mummy's head being rebuilt on Reading Rainbow. Sometimes, the action of film brings something to life in a more dynamic way than photographs or descriptions.
But I do not find much educational value in toddler shows like Miss Spider's Sunny Patch or Little Bear. We watch those shows, but for entertainment. If you watch the Noggin channel, it makes claims that certain cartoons teach "interpersonal and intrapersonal skills" to children. I think that's ridiculous; you learn these skills from actually interacting with people, not from zoning out in front of a cartoon. Also, we haven't found educational value in toddler shows that purport to teach numbers and such, but perhaps someone else has had that experience. I think that, at the toddler/preschool level, the rote "educational" things that TV shows aim to teach can be learned in real life. But to me, the older shows that introduce new places and ideas can have educational value.