From Zipeg Labs:
Zipeg is universal .rar and .zip file opener that works on Mac OS X Snow Leopard, Leopard, Tiger.
If you ever needed just one photo, song or document from the huge archive that has been downloaded or arrived via email - Zipeg is definitely right for you.
Zipeg is tiny but mighty utility. It handles the alphabet soup of variety of archives in addition to commonplace zip and rar. It also does tar, tgz, gzip, bzip2, iso just to name a few.
Zipeg allows you to chose the destination where to extract and merge files (default is your Desktop), intelligently handles the folder names. You can select individual folder inside archive and extract only that folder and subfolders.
Zipeg fully support multipart rar and zip files (those that come in multitude as file.part1.rar ... file.part99.rar) and password protected files (provided that you know the password). It also capable of viewing the photographs by launching preview application and opening other type of documents in associated programs. Zipeg is absolutely free and works on both intel and powerpc based Macs as well as on all flavors of Windows for those of you who uses both at home and at work.