BoxCryptor[1] has been my choice. I've been now using it on daily basis together with Dropbox and I'm satisfied. Boxcryptor works on the client side and stores the encrypted files on Dropbox folder as ordinary files. It is also possible to encrypt filenames. Boxcryptor comes from Germany.
The only drawback I have encountered is that Dropbox limits the path names to 255 characters. With encrypted file/folder names this can become an issue especially with some Java projects.
I think this really gives me the best of both worlds. Security for the files I think need it and the Dropbox infrastructure for syncing files.
Yeah, tried that too. Also tried CloudFogger [1], which has a similar feature.
When it comes to performance, a layer of encryption on top of Dropbox is much better than any competing solution that has client-side encryption built into it, because you're still using Dropbox's awesome infrastructure and lightening-fast sync protocol.
But I ran into the same problem as you did. The 255-char limit sucks, and it's completely unnecessary because even Windows/NTFS allows you to use longer paths (up to 32KB) if you know which APIs to use. I suppose fixing this is not a priority for Dropbox because you normally don't run into it unless you use encryption, and Dropbox has no reason to encourage the use of encryption among their users.
The only drawback I have encountered is that Dropbox limits the path names to 255 characters. With encrypted file/folder names this can become an issue especially with some Java projects.
I think this really gives me the best of both worlds. Security for the files I think need it and the Dropbox infrastructure for syncing files.
[1] https://www.boxcryptor.com/