I'm currently running a character inspired by the Celtic Morrigan and the Norse valkyries (the "choosers of the slain" type, not the Valhalla mead wench type), someone who lives for battle and "encourages" warriors to fight (or flee in terror). She needs a like-minded sidekick, though, someone who isn't merely an oath-bound warrior or a sellsword, but who fights for the sake of fighting.

Jenassa's attitude is spot on, and her "killing as art" philosophy is nice counter-part to this character's "chaos for the sake of chaos" mentality, but I've used Jenassa with so many characters that I'd like to try someone else. However, I can't think of any followers off the top of my head who aren't simply in it for such petty things as money or duty or gratitude. Any ideas?

I usually don't use followers, but what about the one on Solstheim? Teldryn Sero, I think his name is? Granted, he's basically the definition of "merc for hire" so he might not be what you're looking for. Or there's Uthgerd the Unbroken in the Bannered Mare in Whiterun, she can be a follower if you beat her in a fist fight. She might be good for the part.

Anum-La the Swamp Knight from Interesting NPCs always loves to fight, I love her personality, she's probably my fav modded follower despite that mod having a lot of great followers.

Erik the Slayer is in it for the money, the adventure but he does seem to have a personal vendetta against bandits.

But I hardly use vanilla followers... I like custom modded followers more if I am looking for something specific out of them.

Thanks for all the suggestions. I'm not averse to modded followers, so I may check out Interesting NPCs.

I guess I'm looking for a more "dark" character, possibly with a good dose of gallows humor. Was kind of thinking of Cicero or Eola, but not sure if the quests to get them would actually make sense for this character. And not to diss the voice actor, but I'd hate listening to Erik all the time (or Onmund or Sven, or anyone else who uses that voice).

Erik's voice is the reason I hardly use him. if I wanted a boy to tag along I'd look into children as follower mods.

Stenvar, at the Inn in Windhelm, comes to mind.

He's a Nord, so that fits into the Norse stories. And he likes to make comments about wanting to fight something.