Prometheus exporter for sensor data like temperature and fan speed.
lm-sensors (http://www.lm-sensors.org) to get metrics like CPU/MB temp and CPU/Chassis fan speed. You'll likely need to install lm-sensor dev package (libsensors4-dev on my Ubuntu 14 system) in order to build the dependant package github.com/md14454/gosensors.
hddtemp (http://www.guzu.net/linux/hddtemp.php) to get HDD temperature from SMART data. Since hddtemp must run as root to collect this data, rather than call it directly we expect the user to run it in daemon mode with its -d flag. Then we connect to a port it listens on to fetch the data.
See https://grafana.net/dashboards/237 for an example dashboard. This is probably way more than what you want, just mine the bits that are of interest and incorporate them into your general system health dashboard.