disktool is an XView based GUI program,that monitors one or more filesystems and alerts the user when afilesystem has reached a critical threshold of available space.
System Health Monitor is a handy python program that will setup your system to generate RRD Graphs of network interface traffic, system load, memory usage, disk space and inode usage and running processes.
KBMon is a bandwidth-monitor for local network devices. On three different panels you can watch the speed of the transfered and the received data, and you can see the speed of the total data on the choosen interface.