We have a manpage in ./contrib/debian/manpages/bitcoind.1 (surprise!), but it's very out of date.
This is one of the things that will be eternally out of date, and as long as its under contrib/debian it is not up to us to maintain it.
Debian probably has a newer one though, see: https://launchpad.net/debian/+source/bitcoin/+changelog
It could be that it had to be relicensed from GPLv3 last time.
I still think the manpages should become a first-class part of the repository and also installed on 'make install', instead of inside the contrib/debian/ 'ghetto'.
It is possible to generate part of it automatically from --help output.
Also it probably shouldn't aim to list all the RPC commands, as there are too many of them. Also as bitcoind doesn't work as a RPC client anymore in the first place...