There are other services which advertise security, but nothing where you actually are likely to audit the code. Even if their security model is better than what Dropbox is now using, you have to factor in availability issues (Dropbox seems more solid as a business than a lot of the others), functionality, etc. You also need to trust the entire development process, release engineering, and knowing your binaries correspond to the source code. It's not easy.

There is a slight benefit to "must ship trojaned software to recover passphase, then decrypt" vs. "just access data server-side", but in practice, if your threat is the government, there's not a huge difference. If your threat is a server break-in by a third party, then there's some difference.

Overall, probably the best bet, if you don't run your own servers, is Dropbox plus your choice of well tested encryption on top. As for your best well-tested encryption, that's a hard problem too -- Truecrypt has a pretty wide following and some versions have been audited, and source is published. For general purpose use on Macs, I just use Apple's encryption -- it's probably ok, but as far as I know, hasn't really been analyzed by third parties (I'd be happy to NDA and look at it). I rationalize it as if Apple is subverted, and I use OSX, I'm fucked even if third party disk encryption software itself is safe.