Asassins:
Everyone always complains that their "fun" spell isn't useful, like the crusadors'.
Well I found a use for my pet rat, so there :P
(Not exactly sure if rat is behaving as intended, so if this goes away in a few patches, my apologies) This stuff only works about 50% of the time, but when it does, it's nice.
Even though it's a non-combat mob, it's technically "in your group". This has a couple uses:
1) helps you run away
2) helps you backstab
The trick is use Evade and Stalk, because of their agro-reducing abilities. When getting chased by mobs, hit evade, and then run by you're rat as you hit Stalk. About half the time, the mobs will ignore you and attack your rat... buying you some time. Really handy when Sprint is running out.
Likewise, if you don't get to start a fight with a sneak-attack (ie. you get jumped) do the same thing. Evade/Stalk. About half the time (if you haven't built up too much agro) the mob will turn on your rat. Then you can take your time getting behind him for some nice damage.
Also, no he won't taunt, and no he won't do damage in return... but he has some nice HP (I think he levels up with you).
Hope this gives you some new-found respect for the little guy! Have fun!!