SpiderOak (most similar to drive, dropbox), Tarsnap (nix-only, have to compile it yourself), aes.io (browser-based, like box.com)

I've been using JungleDisk for backups. I have it set up to encrypt locally with my key, and the backups are stored in my Amazon S3 account.

Tahoe-LAFS-on-s3 from Least Authority Enterprises https://leastauthority.com

Bonus: one user, 'sickness', showed how to replicate your encrypted data across Dropbox, gdrive, etc. http://www.sickness.it/crazycloudexperiment.txt

HN's own cperciva has created tarsnap.com

He's a crypto expert, so you should check out his service.

Not quite a Dropbox replacement, but Arq for Mac OS X uses S3 for backup, and encrypts your data with a private key that only you know (unless he's surreptitiously sending it to himself).

I mentioned that at Corkboard and mailed the guy about it; http://news.ycombinator.com/item?id=4224524