Mind sear is the kind of spell that is kinda weak for only a handful of mobs and utter silliness (in a good way) with tons of tiny mobs. On some of the spider wing pulls in naxx 25 man my shadowpriest was peaking at over 10k DPS, by spamming one spell.

I think arcane mages are the easiest aoe to box however. just keep spamming a key til stuff dies. Works well with prot pally as mentioned earlier, as well as a holy priest spamming holy nova. Trifecta I was able to achieve higher dps by spamming blizzard, but it's too hard to box that way, requiring too much micro.

FoK rogues are also good for aoe dps, but they are getting a much needed nerf. Sword spinning warriors are pretty good too, albeit on a long cooldown. Just glyph for arcane explosion, gear for spellpower, maybe spirit, you just need your mana to last longer than the mobs, then drink self made water