The Archive Browser is a program that lets you browse the contents of archives, as well as extract them. It will let you open files from inside archives, and lets you preview them using Quick Look.
It is based on The Unarchiver, which means it can handle a large number of different archive formats: It can handle common formats like Zip, RAR, 7-zip, Tar, Gzip and Bzip2, as well as older formats like StuffIt, DiskDoubler, LZH, ARJ and ARC. It can also handle other kinds of formats, like CD and DVD images such as ISO, BIN, MDF, NRG and CDI, many Windows self-extracting EXE files, and can even extract media from Flash SWF files. It will also handle different filename encodings gracefully.
For the curious, it will also show you a lot of information about the archives and their contents.