Save Gabriel petition, which was posted directly after "Hammer of the Gods" aired.
Save the Seeker petition in order to give Legend of the Seeker another season. You can also go to SaveOurSeeker.com and find different campaigns, donations and other ways of promoting and supporting the show. Heck, even Terry Goodkind, the author of the Sword of Truth novels which the show is based around, fully gives his support as well. So even with the announcement of it being canceled there's still hope lingering amongst the LOTS fandom.
This is why fandom exists. It might seem like a long-shot to some but, we've proven multiple times that our voices count and can be heard if we band together and make this kind of noise.