Perl

• The Official Perl Homepage
• Rex Swain's HTMLified Perl 5 Reference Guide
• NCSA Perl Tutorial - Just the basics
• The MacPerl Book Online

LaTeX

• The LaTeX Navigator
• The Penn State TeX/LaTeX Website
• LaTeX Help 1.1

Routines

• Numerical Recipes in C - online and in PostScript form.
• NetLib an online collection of useful routines.