iptables
ipset
tcpdump
mpstat (from pkg sysstat)
free (for RAM)
cat /proc/meminfo (details for RAM)
df -H (fs info)
ncdu
iotop
cbm (networking)
goaccess -f <file.log> (log analyzer)
iperf
dstat (common statistics)
xhprof (php profiling)
graphviz (using with xhprof for creating schemas)
jpegtran (lossless compressing for jpeg)
jpegoptim (lossless compressing for jpeg)
OptiPNG (lossless compressing for png)
PNGOUT (lossless compressing for png)
Debian repositories:
deb http://ftp.us.debian.org/debian/ wheezy main non-
free
uptime
tload (cmd cup loading graph)
route -r (route table)