I just did the quest in Ashbury where you go to the cemetery for Geoffrey Tarellond-Ashe and retrieve the gem that's been making the dead come back as zombies. I understand that Geoffrey is an "evil" character and he can actually become a companion if the player is evil as well, but would there be any consequences if my good-aligned character were to give him the gem? There doesn't seem to be any other options to finish the quest, and I could use the money and the experience points, but I just want to make sure I won't be returning to Ashbury in five in-game weeks only to find that he's massacred the entire town or something.

You can always hand him the gem to complete the quest, and then betray him by murdering him on the spot, and taking back the gem — along with his robes; say, is that real fur? — to sell elsewhere in town. (Just be careful not to let a roaming guard witness your battle.) For even more fun, cast Conjure Spirit on his corpse so you can continue the conversation.

Of course, this means he won't be able to join you later... but to be honest, he's nothing special unless you're already evil and find yourself really really needing a Black Necro/Fire/Force specialist who can also backstab.

From a combat-potential standpoint he's nothing special (in fact, he's fairly useless due to the bad combat AI - mages run headlong into melee instead of casting spells), however he's one of the handful of fully-voiced NPCs in the game, and he has some interesting banter with the other fully-voiced NPCs. From a character standpoint he's well worth the trouble.

You're right, of course. I always forget about that aspect, especially since I rarely go full evil and (more importantly) his VA is so spectacular at portraying him as such a pompous jerk.