One for the Canadians here: The Friendly Giant.
I was brought up on his show, and it was still worth watching as long it was on.
Waaaaaaaahhhhhhhhhhh! When did this happen?! The little chairs in front of the castle, and the giraffe (IIRC) and the rooster and the stories?! I loved that show when I was a kid! [BTW, I’m not Canadian, but the local PBS affiliate used to broadcast the program when I was younger.]
Charles Schultz. 
I grew up on Peanuts books, comics, videos, etc.; Schultz was almost like a substitute grandfather or uncle to me as a child. I’ve gotten pretty jaded and cynical as I’ve gotten older, but when I found out he had died, I cried for the first time in years.
Erma Bombeck…Granted I am her exact demographic but I swear her writing just cracks my chunky butt up!!! I truly miss her writing.
I’ll also second, third and fourth Phil Hartman. Huge talent taken way too soon.
Phil Hartman – Troy I miss you.
Walter Matthau was and is my favorite personality. He had such a dry delivery and sense of humour.
Sorry, screech-owl, Friendly died in May. He didn’t make big headlines (damn kid journalists!), so I just stumbled across the story, but the CBC obituary is at http://www.infoculture.cbc.ca/archives/filmtv/filmtv_05032000_giantobit.phtml, and another at http://www.tvparty.com/lostgiant.html.
It really hurt to hear that he was gone.
Elvis.
And Mother Theresa. Among others.
God, what a depressing thread.
Janis Joplin