I use Wuala. I think their software is pretty nice; don't know how it compares to SpiderOak since I've never used it. They encrypt client-side. Employees can't access data. Or so they say, since the client isn't open source, which is my main hangup.

If I understand correctly, it's not as secure/confidential as Spider Oak: the encryption key for file A is Hash(A) and your own key is only used to gain access to Hash(A) in order to decrypt the files. This lets them deduplicate more efficiently on their end, but it also means they can determine if two users have the same file. It also has some other repercussions (there is a HN story about it). It's still a lot better than DropBox, though.