From Subsume Technologies:
BetterConsole is an application that you can use to display messages written to the console, or any sort of log file. It makes the Console application that comes with Mac OS X look like a sissy. Although Apple's console has come a long way since it was part of the Workspace (e.g., BetterConsole is no longer 25 times faster), it still leaves much to be desired. Some of the features that BetterConsole provides:
Follows multiple files, including rotating log files.
Supports filter rules for ignoring unwanted output.
Advanced control of window hide/show, transparency, and control hiding options.
Added the ability to hide window controls. With a transparent background, this gives the ability to do "desktop" consoles that some people like. We never have enough desktop visible for that sort of thing, but we stuck it in here anyway.
Revamped the document setting inspector.
Removed window transparency setting.
Added a File menu item to open commonly used user and system log files.
Added a Console menu.
Added the ability to update the Dock when there is log activity.
Added an option to not make the window visible on output.
Changed the way window hiding works so that the Window menu now lists even non-visible consoles.
Now supports .log files directly. (Requested by Gregg V. Carroll)
Show entire log file when you begin following it. (Requested by Jason Hill)