Madness, from the mind of Krinkels, is the definitive mass-casualty animated series. Starting with a big marshmallow in 2002, the series has gone on to inspire hundreds of fan animations, fan games, fan art and fan music. We even host an annual event here on NG; September 22nd is Madness Day!
You can browse Madness fan animations by era via these shortcuts:
Krinkels and The-Swain have released Madness: Project Nexus on Steam, go buy it!