MarieMF, have you found a solution to this yet? I took a look at MemberStack (thanks Duncan) and I don't see an option to add content for individual clients. I spoke with Smart Vault yesterday and they are more of a file sharing portal, without the nice UI. I still haven't found something that fits the bill. Wondering if you have had better successs.
I know it's out there because I see client logins for businesses that I know have personalized content. I just can't figure out what they are using.