Here is a list of resources that I found useful in studying different computer languages:

Objective C

GCC:

Make:

XMLRPC

XMLRPC provides quick and flexible implementation for web services.

Perl:

Python:

Awk:

Shell scripts:

GNU Plot:

SQL:

PHP:

Apache:

JavaScript:

HTML:

Tcl/Tk:

OTCL:

GDB:

GProfile:

Latex:

NS2:

Sendmail:

Thread programming:

RPM

Unix Administration topics:

Security

Matlab

Summarized by David Wei Please contact me if you have comments.