OS monitoring tools I should be using?

Is there a good place that summarizes the OS tools I should
be using to monitor postgresql servers on various machines?

On *nix machines I have sar/sysstat stuff constantly logging
stuff; but on Win* machines I don't know what the equivalent
should be. Any recommendations?

For interactive monitoring I have an OK feel for vmstat
and top to watch memory & cpu use, and iostat to watch the
quantity of disk/IO per drive. But there are still some
things I can't find easily so any new advice wold be appreciated.

For example, HPUX's iostat used to tell me number
of disk-seeks/second but I don't see the equivalent for Linux.

Rather than just ask that specific question; I'd be interested
to know in general what OS-level monitoring tools you guys
find most important for various platforms.