Depends on what you want to do. For the web the most common are HTML, Javascript, Java, ASP, PHP, and Perl. For Microsoft Windows one of the most common for beginners is Visual Basic. However, a multi-platform language like C and C++ are what most things are made with. Delphi is not used much, but has a lot of features.
Sourceforge has many projects that are more linux based. Planetsourcecode has examples for a few programming languages. freevbcode.com has many examples for Visual Basic and is a very good site for beginners. Hotscripts.com has a large collection of PHP, CGI, Perl, Javascript, and ASP code, ready to use as is or to get ideas for your own projects.