You could check out
www.tresorit.com . They claim to use end to end encryption, so they should be pretty safe.
Seems cool, but at $10 for 100Gb a month, it's pretty pricey... If you're really into security, maybe you can put your files into a truecrypt container before putting them on dropbox?
You get 3Gb for free. Lifetime.
If that is not enough, yes, you have to pay.
I'd say that's better offer than dropbox have.