Question, are you accessing items via secure vpn? Are you looking to access items outside your network?
The reason I ask, is there are some companies that have cutoff dropbox etc since you can pretty much put anything and bring anything onto the network. This causes security problems.
If you are just looking to edit documents and you don't care where the documents reside then I would say dropbox or another cloud like service. There are a couple really good programs to edit documents and save etc. However if you are looking for version control that window closes as I don't know to many that do version control.
Another option might be a sharepoint site, as you can setup version control and checking in/out of documents etc.
Can I ask, what issues you are having with MS exhange?