QuickLook is the technology behind the handy window that pops up when you hit the space bar in Finder or many other applications. Apple includes preview generators for the most popular file formats; however, there are also a few very useful so-called QuickLook Generator plugins from third parties.

BetterZip QuickLook Generator is a plugin for QuickLook that allows previewing the contents of archive files. The currently supported archive formats are: ZIP, TAR, GZip, BZip2, ARJ, LZH, ISO, CHM, CAB, CPIO, RAR, 7-Zip, DEB, RPM, StuffIt’s SIT, DiskDoubler, BinHex, and MacBinary

http://macitbetter.com/BetterZip-Quick-Look-Generator

Suspicious Package is a plugin for the QuickLook feature of Mac OS X 10.5 (Leopard) and 10.6 (Snow Leopard). It allows you to preview the contents of a standard Apple installer package without launching the Installer

http://www.mothersruin.com/software/SuspiciousPackage/

More Plugins:

http://www.quicklookplugins.com/