In the 1st chapter, note that you can kill the priests of 'Tyr' without going evil: just make sure the guards don't see you. Darkness spells are your friend here.
You can also kill henchmen. I always kill Grimnaw (hey, he wants it) and pick the pocket of Tomi, who will then attack (hypocrite). Make sure you've got their items first (and remember that you can duplicate the rings in Diving Pool, and they stack).
If you attack Grimnaw in the mercenary barracks, the mercs will attack you as well. Don't attack Tomi, at least not in the temple, as the dying patients will become hostile - I watched in horror once as my summoned monster went on a rampage killing them all and doing horrible things to my alignment! Let him start it.
I had problems with the mummy spawning technique as I'd get a free Attack of Opportunity on a mummy going past, making me visible - locking/unlocking the coffin kept my PC busy while I was moving things in/out of the coffin.
A fun one in Luskan is at Host Tower Level Four - the golem rods are unique items, so if you drop them, the Divining Pool in the temple will create a duplicate. Each Replication Rod produces a Helm Horror and you will be rewarded with 50 experience points; sending 20+ Helm Horrors into battle really changes things '> Alternately, you can create the Helm Horrors without using the control rod, and destroy them, but obviously it is easier to drop down to the 3rd level - rather than fighting all of the critters there, I recommend destroying one brazier and then putting a summoned Hound Archon in front of the other. Sit behind an invisibility spell, and go and get a cuppa '>
Wizards and sorcerers eventually don't even need encounters at all; a summoned Balor will attack you if you don't have a protection from evil spell up - and in addition to xp, they regularly drop tiny amounts of loot.
[edit] Oh, two other Divining Pool tricks - at Jhareg's Castle you get a unique key and are expected to chose between 3 doors; by duplicating the key you can open all 3. While back in Chapter 1, when you get notes from the thugs who ambush you after you recover a reagent, you can take it to Fenthick for 50 experience points and 300 gold pieces (+50 gold pieces with a successful persuasion check) - the notes are also unique and so can be duplicated. I recommend doing this at least once for the surreal situation of having Desther being the good guy, trying to warn Fenthick against the scoundrel who is robbing him!