I'd like to recommend Box.com, but if you're specifically changing because of the recent Dropbox DMCA takedown in private folders clusterfuck, then I can't see that they're any different. Box.com has the same encryption setup as Dropbox - they hold the encryption keys and can therefore have access to your data, share it with law enforcement, etc etc. The only difference is Dropbox has started exercising that ability where (so far) Box.com hasn't.
SpiderOak is better in this respect since the full encryption of your data is against a key that you store locally, and they store it in a way that they can't even see your directory structure if they wanted to. However, I tried SpiderOak and it's horrible on OS X, at least. The app drains battery like crazy (not surprising since it appears to be an Adobe Air application), and the sync is very, very slow.
It's frustrating to learn that there is, at least for now, no viable Dropbox alternative that solves the data privacy issue. Here's hoping SpiderOak improves!