Ranks for the Memories: 2000-2009 | The Hollywood Reporter: Top 10 Biggest TV Biz Blunders of the Decade

I think they covered the major ones here. At least ones with specific shows attached. In general, the practice of bouncing a show around, not promoting it, and then complaining about low ratings before using those low ratings as an excuse to cancel it is an all too common process that most networks have taken to. That and letting some shows go on way too long. Either way, good list, give it a look.