Programming tips and tricks for different programming languages

Useful resources to learn new things and/or to avoid re-inventing the wheel.

Shell :
Catonmat - "Awk One-Liners Explained"
Catonmat - "Bash One-Liners Explained"
Catonmat - "Commandlinefu One-Liners Explained"
Catonmat - "Perl One-Liners Explained"
Catonmat - "Sed One-Liners Explained"
Catonmat - "Unix Utilities You Should Know About"
/r/linux/ - "Give me that one command you wish you knew years ago"
StackOverflow - "Hidden features of Bash"
StackOverflow.com - "Hidden features of Windows batch files"

Bit manipulation :
Catonmat - "Low Level Bit Hacks You Absolutely Must Know"

Sean Eron Anderson - "Bit Twiddling Hacks"

C :
StackOverflow : "What is your favorite C programming trick?"
StackOverflow - "Hidden features of C"

C++ :
StackOverflow - "Hidden features of C++"

Python :
/r/Python/ - "What's the one code snippet/python trick/etc did you wish you knew when you learned python?"
StackOverflow - "Hidden features of Python"

C# :
StackOverflow - "Hidden features of C#"

Delphi :
StackOverflow - "Hidden features of Delphi"

Java :
StackOverflow - "Hidden features of Java"

Javascript :
StackOverflow - "Hidden features of JavaScript"

HTML :
StackOverflow - "Hidden features of HTML"

Ruby :
StackOverflow - "Hidden features of Ruby"

PHP :
StackOverflow - "Hidden features of PHP"

Perl :
StackOverflow - "Hidden features of Perl"

CSS :
StackOverflow - "Hidden features of CSS"

VB.Net :
StackOverflow - "Hidden features of VB.Net"

Misc :
/r/AskReddit/ - "what are some computer tricks everyone should know"
/r/AskReddit/ - "What is one cool internet trick you've learned?"