Komodo Edit from ActiveState is a free, open source, multi-platform, multi-language editor (PHP, Python, Ruby, Perl and Tcl, JavaScript, CSS, HTML and template languages like RHTML, Template-Toolkit, HTML-Smarty and Django).
Background syntax checking and syntax coloring catch errors immediately, while autocomplete and calltips guide you as you write. Available on Windows, Mac OS X and Linux. XPI extensions allow you to create your own plug-ins. XPI extension support provides the same capability as Firefox, with all standard Mozilla APIs based on XUL, XBL, and XPCOM, plus our own for Python and JavaScript. Other features include Vi emulation, Emacs keybindings, code folding and code snippets.