The most important kernel parameters can be found in the
tunable parameters guide.
It's focus is Solaris 8 but sufficient history is included to make
the guide extremely useful for earlier releases.
There is also a large number of kernel variables of which the main
purpose is debugging and testing or even disabling of new(er)
algorithms that are seen to be risky. Such variables are typically
not documented, except in workarounds when problems do arise.