Hide a running app from Dock?
Important Note: In Mac OS X 10.5+ the method explained below only works for apps which are not using the "Code Signing" feature which was introduced in 10.5 to ensure authenticity of running code. The result of applying this method to a signed app differs; it might cause the app to  crash upon starting or results it unexpected behavior.

You can edit the file Info.plist contained in the directory of each App (e.g. /Applications/VLC.app/Contents/Info.plist)by adding the following lines:

&lt;key&gt;LSUIElement&lt;/key&gt;
&lt;string&gt;1&lt;/string&gt;


For example:

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;
&lt;plist version="1.0"&gt;
&lt;dict&gt;
        &lt;key&gt;LSUIElement&lt;/key&gt;
        &lt;string&gt;1&lt;/string&gt;
        &lt;key&gt;BuildMachineOSBuild&lt;/key&gt;
        &lt;string&gt;11G63&lt;/string&gt;
        &lt;key&gt;CFBundleDevelopmentRegion&lt;/key&gt; 
        ...
        ...
&lt;/dict&gt;
&lt;/plist&gt;


When you will start the App you will see the icon just for one second and the it will disappear.

Dockless and Dock Dodger do this change automatically in apps.