I have used http://www.strongbox.io/ - it allows you to create a 'box' of passwords or other data that is securely shared with other users.
"Your password never leaves your phone or computer and is not stored anywhere. Encryption occurs locally. You are the only one that can decrypt your data!"
square with
"Anywhere, anytime access. Access on the phone, web or desktop. All apps work in offline mode & auto sync when connected."
If they provide a web interface, they'll probably get access to my key at least temporarily (unless they decrypt in JavaScript and I trust them to not hijack this). GPG + Dropbox seems a little less convenient, but significantly safer since I have full control over the encryption process, especially in view of the fact that the US seems to be keen on listening in on cloud data of non-US citizens.