Extend Quick Look for folders and archives
Without any tweaking, Leopard's Quick Look feature shows you a full-size preview of almost any file without opening an application: As you're browsing through files in the Finder, simply tap the space bar. But there are two free plug-ins available for Quick Look that extend its functionality and usefulness.
The first is for folders. By default, when you look at a folder with Quick Look, you see some general information about the folder and its icon.
But with the Folder Quick Look plug-in, you can also see a list of the folder's contents (optionally including all hidden files) as well as information about each item such as file size, creation and modification dates, and file type.
Similarly, Zip Quick Look Plugin allows you to peer into .zip archives. This makes it easy to see what files are contained in an archive from the Finder or within an attachment in Mail. Being able to get a view of the contents of an archive before expanding it makes it easier to work with compressed files, but it also adds a certain level of security (particularly when used in Mail) because you can ensure that the contents are something that you actually want to expand and/or open.
Add canned searches to the Finder sidebar
The Search For section in the Finder's sidebar in Leopard gives you convenient access to any number of Spotlight searches. Apple packages a handful of these into the sidebar by default, including searches for all files modified on today's date or within the past week.
As helpful as these searches may be, adding custom searches to the sidebar can make this feature even better. Any Spotlight search can be saved to the Finder's sidebar.
To create a detailed Spotlight search, use the Find command from the Finder's File menu (or the Command-F keyboard shortcut). You can designate specific locations to search and whether to search the contents of files or just their file names.
You can also string searches together from a variety of file metadata -- information that is appended to files by applications, the file system and Spotlight itself.
The most common options to search for, beyond a simple string of text contained in file names or contents, include the type of file and the date a file was created or last modified.