Contains spoilers:
Well some obvious things are killing Adalon (silver dragon) for the human flesh armour. Killing Drizzt and his gang. Doing the buried alive quest evilly (don't forget to go back to the house after collecting the ransom to kill some cowled enforcers
). Killing Valygar then using his body to do the Sphere (also can kill more cowled enforcers in his town house after this
). Backstabbing both Matron mother and Phaere then using the eggs to get a halberd. Side with Bodhi. Don't save Aerie from the illusion (or even kill her
) Do a deal with Firkraag then kill him when you're good and ready. Do the hell quests evilly. Kill Keldorn and Anomen
.
Some quests it doesn't pay off to be evil, like the Trademeet druid quest - if you act evilly (poisoning the grove) you don't get the subsquent quests.
Some things you surprisingly don't lose reputation for, like killing everyone in the radiant heart (I did this, but loaded because I felt so guilty
).
You can steal from most people, except Ribald. But you can pickpocket him.
A lot of quests you can't do evilly, like the Fallen Paladin quest, Nalia's keep, Haer'dalis's quest. But you can rationalise that you're getting booty from them