And there's always the ubiquitous
mbmon port that can get CPU temps, MB voltages, and fan speeds ... if the MB has any supported monitoring chips.
You may need to load some
smbus modules to get the full range of monitoring capabilities. Have a read through /usr/src/sys/<arch>/conf/NOTES and /usr/src/sys/conf/NOTES for which smbus-related modules to try loading. (<arch> is i386 for 32-bit installs, and amd64 for 64-bit installs.)