Ok here's my contribution, I have never seen such a crowd for the sunday services before. Apparently most characters are sinners...
The sins:
Lisa - Read "peccable" literature (No further comments)
Grandpa - Feeding the park animals (Strictly forbidden according to the hospital rules)
Reindeer/Birds - Gluttony
Apu - Worship pagan idol (Lust?)
Otto - "Work" on bus (i.e steal parts from bus, hence greed)
Hibbert - Surgery using organs from his black market business (Greed)
Martin - Try to be cool (Pride)
Nelson - Mocking Ned (Wrath)
Skinner - Spying on Edna (Lust)
Ned - Condemn Science (this must be a sin!)
Fat Tony - Get rid of a "problem" (The result of wrath)
Wiggum - This "woman" obviously spend too much time on her looks (Pride)
Edna - Smoking (Gluttony ;) )
CBG - Read "peccable" literature (No further comments)
Barney - Sleep in the gutter (No further comments)
Mayor Quimby - embezzle money (Greed)
Moe - Spying on sunbathers (Envy)
Burns - Hid nuclear waste (Greed)
Brockman - Laziness (Sloth) and consumption of alcohol
Bart - skip school (Sloth)
Homer - Lounge in the pool (Sloth) and consumption of alcohol...
Smithers - Hideous drunken wreck (No further comments)
Milhouse - Fly scale model, not sure what sin this is but he has always made me dizzy and Smithers will soon feel his wrath...
Bumblebeeman - He has obviously been stealing honey (Greed)
The bees chasing bumblebee man - Uncontrolled anger (Wrath)
Snake - Rob Kwik-E-Mart (Greed)
Krusty - Inflate his own importance (Pride)
Cletus - "Steal" garbage (Greed)