In no particular order:
MTV (and while we're at it, MTV2, which has essentially become a carbon copy of MTV1)
VH1 - It has essentially become Viacom's version of E! in recent years instead of being "Music First"
ESPN Classic - Bowling, the World Series of Poker, reruns of "American Gladiators", "Stump the Shwab", and "Arliss", don't constitute as being "classic".
G4TV - Has gone right down the toliet ever since Neal Tiles was put in charge.
The Disney Channel - It used to be a general audience channel/tribute to classic Disney animation and productions. Now, they've completely sold out (dumping "Vault Disney" in the process) and is a strictly tween/"Let's milk the cash cow dry" (a la "Hannah Montana" and "High School Musical") fare.
Nickelodeon