lsof     - list of open files
free     - free OS memory
file     - identify file type
basename - extract base name
htop     - advanced top
atop     - http://www.unixmen.com/linux-basics-monitor-system-resources-processes-using-atop/
iotop    - monitor io (http://www.tecmint.com/install-iotop-monitor-linux-disk-io-in-rhel-centos-and-fedora/)
vmstat   - memory mon
inotify-tools - inotify wrappers
watch    - run the command every n seconds (-n 1)

du
df

iftop    - net util-n
netstat
nethogs