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/