Trawling through and editing code can be loveless task. TextWrangler is a free app from the Mac App Store that could make it just a little bit more bearable.
Brought to you by Bare Bones Software, the folks behind Yojimbo and the incredibly powerful BBEdit, the free TextWrangler is pretty intuitive and feature rich. Starting out as BBEdit lite, TextWrangler is a fully fledged editor in its own right. You've got pattern matching, full search and replace, syntax highlighting for quite a few source code languages, code folding, which compresses the code down to a more manageable length, and many other text manipulation and batch processing features.
The interface is pretty simple to navigate with most needed tools available via an icon or keyboard shortcut, plus there is some decent text color-coding that makes reading code a little easier. You can open and save over FTP and SFTP, streamlining HTML authoring. TextWrangler even has support for both AppleScript and Mac OS X Unix scripting, making batch processing easy.
Whether you're looking for a decent editor for HTML, CSS, XML or anything else, TextWrangler is a great free starting point. If you're just looking for an editor for writing plaintext files, a replacement for TextEdit, or modifying XML, .plist files or something similar, then TextWrangler is more than up to the job.