Well, not quite a mod, but a modified "particles.png" changing the "puff" effect that happens when something dies into a bloody little explosion. For those unintelligent enough to do it themselves, here you go.
Add this little pic to your favorite texture pack or replace it in the "minecraft.jar"
Add this little pic to your favorite texture pack or replace it in the "minecraft.jar"
http://www.youtube.com/user/GoodManLouieDog