What Are the Biggest Publishing Houses?

I didn't really know where to put this thread, but I figure here's as good as anywhere. I am looking for the next round of agents to query. And while I have an idea of where I'd like to publish (Henry Holt), I'd obviously be ok with any large publishing house. So when looking at agent's sales, I'm wondering if I'd know the best publishing houses if I saw them. I obviously know Random House and Simon and Schuster but recently I saw someone say they'd love to be published at Avon and I wondered, is that a big house? (Maybe they just want to be published there like I want to be at Holt even though they're not the biggest). But it occured to me, due to a very eclectic and not terribly recent personal book collection, that I may not know the big names when I see them.

Anyway, if anyone would be so kind as to list maybe the top 10 biggest publishing houses, so I'll know them when I see them when looking through agents' recent sales, I'd very much appreciate it.

See now, some of those I haven't even heard of. I know every way to research an agent, but not any way to research the size of publishing houses. Anyway, thanks for helping me with my name recognition issues.

Yeah, the imprints are the hardest part! But thanks for clearing that up too. At least if I know the names of the parent companies, it'll be easier to find out their imprints rather than vice versa.

Wow, what a neophyte I was when I posted this! How funny =)

Anyway, since you've resurrected my dead, and slightly embarassing thread, I feel obliged to answer your question.

They do not accept unsolicited manuscripts. And they say so here: http://www.henryholt.com/imprintsubmissions.htm