Mary Kay Bergman (A.K.A. Shannen Cassidy) was an extremely talented voice actress; One of the most talented actresses I have heard. She played so many people on South Park, that I can't even name them all. Also, she did a good job as Timmy Turner in the "Oh Yeah! Cartoons" shorts. So why in the world did she commit suicide? In the newer episodes of South Park, all of the female characters in South Park sound very naggy and very annoying. Eliza Schieder and Mona Marshall (A.K.A. Sally Evans) were okay, but April Stewart (A.K.A. Gracie Lazar) just can't match Bergman's wonderful voices. I also think that she did a better Timmy Turner than Tara Strong can do.
Overall, she was a wonderful voice actress, who died way before her time.