If the command line is not your thing - here's a GUI front-end for unrar.

UnRarX is a Mac OS X Cocoa application that allows you to expand rar archives and restore corrupted or missing archives using par2.

Drag-and-Drop extraction. Built-in par2 recovery. Written by Peter Noriega.

See the About UnRarX menu for more info. Based on unrar 3.60

What's New:

• Universal Binary version of UnRarX is now available.
• Version 2.2 includes current universal binary versions of unrar and par2 command line applications.
• UnRarX now includes automatic update functionality thanks to Sparkle Framework by Andy Matuschak.