Well, here is a list of the companies that paid to exhibit at the most recent (2011) Joint Statistical Meetings. This includes a lot of publishers. I am not sure why a major publisher would not be at the biggest statistical meeting in the world, or at least at the largest one to draw a lot of different teachers and researchers from a large span of areas.
There's Springer, OUP, Sage, Wiley, W.H. Freeman, Elsevier, CRC, SIAM, CUP, BEP...
Did I miss anyone?
Note that some of these are conglomerates and may have different publishers or different series under the same umbrella firm.
By the way, O'Reilly is not a major statistics publisher. While I have a lot of their books, I don't turn to any of them for statistical insights. I am not sure they have any statistical editors, for that matter, but they do a good job on books on programming.