I found a firewall/orb sorcyn to be quite effective, and that was without an infinity. I know it's kind of out there but with 400+ mf my firewall did over 8k a second and my orb was doing 700something. I could solo anything.

Diablo, Duriel, and Baal were all easy. Andy and Meph were kinda challenging a tad bit. My merc kind of sucked, but if you had a good tanking merc you could very, very easily defeat any act boss. Oh also, I always had to lead Lister away from the throne because he's very often fire/cold immune.