You can enhance the QuickLook feature of Leopards Finder to display a lot more file types. This is done by QuickLook plugins you simply drop into the /Library/QuickLook folder.
I installed three additional plugins to quick look inside archives (done by BetterZip), show contents of folders and color highlight the syntax of certain source files (shell scripts, html pages, perl scripts, apple scripts etc.)
This is what color code plugins result looks like on a shell script:
This is what the content of a zip file looks like with the BetterZip plugin:
You can find a list of QuickLook plugins at http://www.quicklookplugins.com/