I used Ka-Blam for my volume release. Good quality stuff, but US based. They're also a really good choice for smaller orders since you're able to order as little as one copy (I did that in order to have a proof before putting in my big order). They have great customer service and will even do Kickstarter fulfillment for you if you ever need to get that done.
The only downside to them is that they're not very customizable (you can't choose the paper type, finish, etc.) and their price per book does not go down after 500 copies. (So if you order 1000, you're paying the same price per book as if you were ordering 500) Obviously that doesn't become a problem until you need a huge order though!
I haven't ordered through them yet, but Print Ninja is really good from what I've seen as well. They have a ton of options and can do custom sizes, papers, finishes, even spot UV or gold/silver lettering. They're really expensive for small orders though, so I figure I'd transition to them if I decide to do 1000 copies on my next book order. What you SHOULD get from them is their free sample package, which includes a few books they've printed and a booklet that has a sample of every single kind of paper and finish they offer. It even explains how to set up your files for print and what the differences are in some settings. It's honestly really helpful, even if you don't end up ordering from them.
