The “Subversion book” (Version Control with Subversion, written by Ben Collins-Sussman, Brian W. Fitzpatrick, and C. Michael Pilato) is published by O'Reilly & Associates, but is also available online. The online version will reflect any changes in the most recent release of Subversion.
There's also a really nice book by Garrett Rooney (another Subversion developer) called Practical Subversion (published by Apress)
I have both books and use them both fairly regularly. My overall impression is that the O'Reilly book is really good at explaining what's happening “under the hood”, and that Garrett's book is more useful for day-to-day stuff (and has a lot of material on “best practices”—how to use Subversion as a communications tool to keep everyone in the loop about what you're working on). Garrett also did a video talk on Subversion best practices.
There is a printable manual, generally referred to as “Cederqvist” after its primary author, available online for printing. O'Reilly & Associates also published a book called Essential CVS, by Jennifer Vesperman, which is supposed to be quite good.
We don't currently support the use of other revision-control systems, although you are welcome to use them on your own.