Classes with good tank synergy are any strong aoe class that has quick, powerful aoe abilities. If you do not have a tank that can grab a large amount of mobs then look to plate dps as they can take a good beating.
I've had success as a 110 duo with my outlaw rogue (aoe setup), arcane mage, balance druid, and havoc DH paired up with any other strong dps class. I've had solo success on my ret paladin (prot does well, too) and my unholy or frost DK.
If you're a duo then stick to 2x DPS only, imo. You really don't need a tank/healer if you can figure out your max npc pull amount for each dungeon. Some dungeons have NPCs that will cause you much more problems than others if not killed quickly so having single target burst is also important.
I would imagine warrior would be a very strong duo class. They offer great aoe, self buff, mobility and even some decent CC options.