DISCLAIMER: This type of character is so powerful it has the potential to ruin the fun of the game. I don't recommend it unless you've already played through Arcanum at least a couple of times.
The Solo Halfling Stun-Assassin:
Halfling (Half-Orc also works)
Troll Blood
Put 1 point in WP
2 points in Mental Magic for the Stun Spell
1 point in Melee
1 point in Backstab
Buy a dagger at character creation
You can now mercilessly slaughter almost any creature in the game. Simply Stun them, move behind them, and Backstab them. Repeat until only steaming piles of entrails remain.
The only things to watch out for are Stun immune creatures, of which there are very few, and getting mobbed early on. Otherwise, you have almost godlike combat prowess.
You'll want to go all or almost all Magick, since there are lots of nice items for thieves. Also, this character will be so reviled by everyone he meets that some NPCs may attack on sight (including some of the city guards in Tarant). However, there are ways to diminish you reaction penalty enough that this doesn't happen, if that's what you want.).