There really are no all-in-one ass kickers (with the exception of the 55-invincimonk, but they are only good for a very limited selection of farming). ANet has done a very good job of making the game very group dependant. Everyone working together doing their thing correctly = ass kicker. Don't fall for that monk crap, it's absolute BS. You don't need a monk secondary to heal yourself, that's what monk primary's are for! That's my personal take on it, but unfortunately 99.9% of the warriors you will see out there are W/Mo because they are senseless and all they know how to do is sever artery, gash, healing breeze, rinse/repeat. Most of the damage comes from nukers (elementists), but AoE was nerfed last update and monsters will run away from AoE now, so it's less effective than it was before.
Necromancers are mainly used for Minion Masters/Mancers (MM for short). Basically you wait for stuff to die and make a little undead follower out of the corpse, eventually you get an army (literally) of undead minions following you around and killing stuff in .5 seconds.
I'm fairly sure that I am the only W/Me that exists in Guild Wars. I think I may have seen about 2 others in my time playing, that being said, they kick ass. He was shakey at first, but once you get it down/figure out your style, you rape stuff. People think it's a worthless combo, I'm out to change that!
Here's a screen shot of my completely ineffective and estranged build... in his shiny new 15k platemail armor...
All in all it really boils down to personal preference, play around with a bunch of different builds, see what you like and what you don't like, look up skills/builds, put together your own style from that. W/Me is really the only build that I have thoroughly enjoyed playing so far in the game, pure healing monks are fun too, and you never have trouble finding a group with one.