SpiderOak are offering unlimited backup space for life for US$125 per year.
Their usual pricing is around US$10/mo per 100gb, so depending on how much data you have this could work out to be a pretty sweet deal.
Offer ends 3:59:00 pm EST Tuesday, April 1, 2014
Unless you're storing more than 1TB in the cloud, Google Drive looks like a better deal at $120 per year.
Edit: I notice that SpiderOak actually wrote a blog post a few years ago detailing why Unlimited storage plans are not a viable business model.
https://spideroak.com/blog/20110202135038-whaaaat-unlimited-…
Does this means they are now building an unviable business?