Bobby - Supernatural
Bobby as close as anyone could be to Sam and Dean, so it's no surprise he wouldn't want to leave when he was killed. He hung around a while trying to help until the boys finally urged him to find a better place. He can still come back once and again.
The Kerbys - Topper
George and Marion Kerby were a couple of ghosts only grumpy, uptight banker Cosmo Topper could see. They just wanted to get him to enjoy life a little, but that normally didn't work out so well.
Bonnie - The Vampire Diaries
The number of ghosts on The Vampire Diaries is almost embarrassing, considering how many of them have been resurrected, and were already other forms of supernaturals anyway. Bonnie got the worst of it, and even went to her funeral before spending a season dead.
Jimmy - Rescue Me
Jimmy Keefe was Tommy Gavin's cousin who died at Ground Zero when the second tower fell. Tommy was haunted by Jimmy throughout the series. At times he was the voice in Tommy's head, and others it was hard to imagine he wasn't really a ghost.
Nate, Sr. - Six Feet Under
The entire Fisher family was haunted by patriarch Nate, who died in the premiere. Whether he was the voice of reason, helping them through tough times or pushing them to do something they wouldn't otherwise do, he was always with the family.