How can I extract .rar files on the Mac?

Using Homebrew, in a terminal type:

brew install unrar

to use it just navigate to your file and type

unrar x <filename>

Or list files via unrar l archive.rar and extract single file: unrar e archive.rar folder/file.exe desired_location/

The Unarchiver really does it's job well (and it's also completely free). From the site:

Supported file formats include Zip, Tar-GZip, Tar-BZip2, RAR, 7-zip, LhA, StuffIt and many other more and less obscure formats. The goal is to make The Unarchiver able to extract anything you give it. The Unarchiver uses the libxad unarchiving library to support many older, obscure formats.

Just for completeness: Fink, MacPorts, Rudix and Homebrew provide versions of the command-line unrar.

The Rudix version is a binary, which means that you don't even need XCode or GCC to install it.