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.

Select "Other" in the search criteria pop-up menu to choose from a treasure trove of additional possibilities, including:

The file label assigned to items in the Finder
The album or artist information assigned in iTunes
Support for specific foreign languages in items
The number of pages in a document
All manner of information included by digital cameras, such as camera model or whether a flash was used

To build a search that relies on multiple criteria (all image files that were created in the last month, for example), hold down the Option key as you're making your selections.

To save a search for later use, click the Save button in the upper-left of the search window and in the Save dialog, choose to add it to the sidebar.

If you want access to more searches in the sidebar, but don't want to expend the time and effort to create them yourself, you're in luck. Apple ships a number of prepackaged Spotlight searches with Leopard that don't appear in the sidebar by default; these can be added to the sidebar in a few easy steps.

Change the log-in window
Leopard's starscape backdrop for the log-in window is pretty spectacular, but how about using a picture of the family dog or a favorite vacation memory? Visage ($9.95 from Sanity Software) makes it easy to change not just the background behind the log-in window, but also to customize the window itself.

For example, you can insert a customized message for you or your family -- or in a business or education environment, an acceptable-use policy or new user instructions. Another option: Replace the Apple and Mac OS X icons with pictures of your own.

Visage, which you can try for free for seven days, has some other cool features. You can set a screensaver as a "desktop effect" that displays continually in the background while you're working, instead of a static desktop picture (really great with some of Leopard's new screensaver options).