Every linux user is familiar with (h)top to monitor processes for cpu usage. Its spin-off tools are a lot less commonly known: iotop for monitoring io,iftop for monitoring network traffic, ftop for file monitoring.. (am I missing any other?).
Another interesting one, particularly if you’re on a mobile device, is powertop for monitoring power consumption. I remember when Intel announced its work on a smaller energy footprint for Intel devices back in 2007 but forgot about it since my kernel didn’t support it yet anyway. 🙂
Although the research was focused on Intel hardware, it is quite useful for other cpu’s like AMD. In that case, powertop is not able to calculate the power usage, but it can still show the number of wake-ups per second per process and how much time is spent in each power state.