What about a ghost/ spirit themed warrior skillset? You could be a ghost or a person channeling (or being possessed by) the spirits of warriors (or fallen heroes)
Mutations. Mutations always work. Expose your berserker to some toxic greenish acid (Dredmor has some) and bling! That would be a skilltree focussing on lots of brawn and resistances, providing faster regeneration and stuff like that. However, toxic sludge has made our mutant hero a) blind b) deaf and c) incredibly stupid. He is barely able to wield a weapon, but if he does, the dungeon shakes. As a skill tree: The lower levels would provide some needed resistances like toxic, putrefying, fire... Perhaps another healing proc when you get hit, and they would lower magic power, savvy and other smartness-related stuff. Not too much, the first levels are basically usable for anyone, rounding out characters with some resistances and a bit of healing. It could get interesting in the higher levels: High penalties to dodge, crit, savvy, magic stats, and in return big bonuses to burl and melee, and some more resistances as well as armour absorption. To keep with the theme of primitive, stupid beast: Very few or no active skills at all, but more passive procs (blisters popping, radioactive punches etc...) That tree would round out builds at lower levels, but you need to plan for it if you want the higher levels.
A couple of less serious ideas, barely fleshed out: Princely Ponce: Your royal blood just makes you better than everyone else. Some stat bonuses, gifts of money and/or items upon levelling up, possibly a "Throw Down The Gauntlet" ability, possibly the ability to order monsters around for a brief period before they realize you're not their prince(ss). Dramatic Backstory: As you level up your dramatic backstory is revealed. Orphaned in a blizzard, betrayed in a volcano, etc. Perhaps it can give contingent buffs when you take certain types of damage, drink potions, or whatever else reminds you of your dramatic backstory. Ideally it would also have some kind of Emomancy synergy.
Cyborg. Powerful attacks and weaknesses, plus some extra . A "Complete the Circuit" buff which deals to attackers and you when hit. Healing that scales with (you're repairing yourself). Other such things.
Sneak preview: four 24 stances. 8 active abilities. 32 192 spell effects (note: each spell effect has more underlying effects). Can you handle the madness?
Four hundred and twenty-four stances?!?!?!?!?!!!!!oneoneone!!11!!!??????//??11/!?!?!/1/1wonwon?QQ????
There's meant to be a strikethrough on the 4 :\. Moar update: Possibly the first scaling buffs in the game, depending on if I can get it to work.