Well, I'll add my list of software favorites for the Mac.
For RAR files, nothing beats UnRarX for decompressing RAR files. It's quick simple and the fastest UnRARer:
http://www.unrarx.com/For media playing, I've found that VLC isn't as dependable as it used to be.
So for all your video playing needs, Perian is the best. It allows you to play any format with Quicktime, so you don't need to install any other media players. I find MPlayer to be finicky and unstable.
You can get the awesome Perian plugin from:
http://www.perian.orgFor torrents, well the pickings are slim. Transmission has given me problems in the past with corrupt chunks. I used Azureus (now it's called Vuze) for the longest time because I hated all the other torrent clients. Well, the good news is that the new Mac version of µtorrent has been officially released. It's so much faster than other clients and more stable too. I'm loving it.
µtorrent for Mac:
http://mac.utorrent.com It's for Intel Machines but some people have gotten reported it works on PPC Macs as well, though it's officially unsupported as of yet.