nmon - This systems administrator, tuner, benchmark tool gives you a huge amount of important performance...
strace - Trace system calls and signals. A diagnostic, debugging and instructional userspace utility.
iftop - iftop does for network usage what top(1) does for CPU usage.
htop - htop - an interactive process viewer for Unix. This is htop, an interactive process viewer for Unix systems. It is a text-mode application (for console or X terminals) and requires ncurses. Latest release: htop 2.
vtop - vtop is a graphical command-line tool that uses unicode braille to chart CPU and memory usage.
ftrace - A function tracer for the Linux kernel.