You can download Wow Cataclysm client here for free!
Cataclysm Mini-client is a smaller file to download but rest of the files will download while you are in game. Note that this can introduce some Ping and other minor issues, but its kinda playable while leveling.
Windows Cataclysm (4.3.4) clients:
Full Clients Direct:
Full Clients Torrents:
Check out our Cataclysm server list