All big software companies have their own sites of libraries and documentations , but when we are writting code we need quick reference or quick solution to problems.
Here are few links which I have used very frequently and are really very usefull.

Oracle Development

Oracle Call Interface, nice tutor

OCI Faq from OraFaq

Oracle SQL and pl/sql and Scripts FAQ

Features added to Oracle Database since 7.0 upto 9.2.0

Calling External routines from PL/SQL

Code samples from Oracle on different technologies

HIgh class Oracle articles and scripts

Oracle Internal notes

Oracle Advanced Performance Tuning Scripts

Oracle Performance Tuning Tips

Unix Shell and Perl scripting

Tao of Regular Expressions

A wonderfull SED startup and advanced guide on IBM's site

Handy one-liners for SED

A wonderfull and detail SED guide

KornShell Memento - Very Nice reference for Korn shell

KSH Manual Page

A nice FAQ on KSH from kornshell.com

The GNU Awk User's Guide - Table of Contents

Awk by example from IBM's site - Good for starting and advance

vi Reference

Robert's Perl Tutorial

Rex Swain's HTMLified Perl 5 Reference Guide

Perl Resources from Perl.com

Signal programming in Perl

Perl in 20 Pages

Perl variable scoping ( Namespaces )

Java

The Java Tutorial

Thinking in Java - The best book to read on Java

Networking in Java

Brief and quick tutorial on JDBC

Good and quick on JDBC

Web server technologies

Apache HTTP Server Version 1.3 Documentation

Conceptual Architecture of the Apache Web Server

Overview of HTTP protocol

Notes on the Security of a UNIX Web Server

Network Firewalls

Browser side Web

HTML Tag Reference

A User's Guide to Style Sheets

Electronic JavaScript Reference

Free JavaScript material

JavaScript detail Guide

JScript ( Microsoft Javascript )

Programming , mainly C

An Introduction to Socket Programming

Automating Program Compilation - Writing Makefiles

Brian W. Kernighan Programming in C A Tutorial

Programming in C

Windows Sockets A Quick And Dirty Primer

Function Pointer in C and Cplusplus

Fundu C FAQ

UNIX network programming: A practical approach

Simple one on Interprocess Communication in Unix

BSD Sockets ( Detail with example )

Unix concept library

Unix system programming

Bjarne Stroustrup's homepage

The C Library Reference Guide

Complete libc.a Reference

Beej's Guide to Network Programming

How the stuff works ?

GNU C Library

Write dynamically loadable libraries

Program Library HOWTO

C++

ANSI C++ Developer's Handbook

GNU C++ Library Handbook

C++ standard library

Cplusplus.com Tutorial

cplus.about.com

OOPweb.com , wonderfull resources

Active Server Pages

ASP tutor and Object reference from w3schools.com

Microsoft's ASP tutorial

Do not underestimate , its MS-OFFICE

MS-Office Developer's Forum from Microsoft

Some tips on MS-Excel

Scientific and Engineering applications of MS-Excel

Site of huge Excel links

More Excel resources

SYBASE

Sybase 11 Unleashed

Sybase Db-lib programming

Pages where we find material of all technologies/softwares

Huge collection of Computer books online , I bet you cannot read half of them

Read XML books online

Complete Technical Books online and that too FREE

HERT ( Hacker Emergency Response Team) Tutorials

Computer Technology Documentation Project

1001 Tutorials - Programming tutorials

Web Developer's Journal

Huge collection of HTML / Web programming resources

Library of books

Yet another Library of popular books, but FREE online

Another library of books to read online