If your copy was purchased through Steam, you can obtain Torchlight II through the Steam client. A Steam demo is also available.
To download the standlone Torchlight II demo, or if you purchased via torchlight2game.com and perfectworld.com, you can use one of the two links provided below.
Torchlight II Stub Installer
22.3 MB (md5: 1F3A4D0AA2995BC5936705072B8FE43D)
Torchlight II Full Installer
1.49 GB (md5: 7D845EBE2CADCAD649B57AF84F0A8BD5)