IDE: Eclipse http://www.eclipse.org/

Ruby (less intrusive to Eclipse): Dynamic Languages Toolkit - Ruby Development Tools

Part of Eclipse’s software updates.

http://download.eclipse.org/releases/indigo

Ruby (Aggressively modifies global settings in Eclipse): Aptana Studio 3 http://www.aptana.com

Aptana Studio 3 is a pretty good plugin for ruby dev

Stable: http://download.aptana.com/studio3/plugin/install

Perl: EPIC http://www.epic-ide.org/

Plugin for perl developers

Cutting edge: http://e-p-i-c.sf.net/updates/testing

Stable: http://e-p-i-c.sf.net/updates

Python: Pydev http://pydev.org/

Plugin for python developers (Included with the Aptana Studio 3 plugin)

Cutting edge: http://pydev.org/nightly

Stable: http://pydev.org/updates