iTerm is my favourite terminal program. It is a great replacement for built-in OS X Terminal.
The only issue I have with its current icon is that there are so already a lot of blue icons on the Dock. I’d rather I have a different color. Fortunately, iTerm resources page has an “old face” black iTerm icon: http://iterm.sourceforge.net/resource.shtml
I used to replace application icon by editing its .icns file but there is an easier way: Mac 101, Lesson 6: Change My Icons