There are plenty of builds that you can successfully use in the solo edition, especially with the recent difficulty reduction.
Possibilities:
WW barb with 1 point in Berserk (as already mentioned)
Shapeshifting druid (I'm currently playing a Frostbite Wearbear, lots of fun)
Zeal paladin
Martial Arts assassin (weapon block + fade + CoS = pretty good tank, just no life buffs)
Summon necro with CE
With all these characters, your best bet is probably an Act1 physical merc, as they have the potential to pump out huge damage and, for the most part, are intelligent (i.e. don't run into packs of death machines like Act2 mercs tend to). However, all mercs have their place, so it depends on your build/style.
Let us know what you're thinking of so we can start tossing out build ideas