Password managers such as Lastpass along with a 2-factor auth for each user should be pretty good (preferably not SMS-based as these can be relatively easily bypassed with SS7 access, but based on Yubikey-like hardware tokens or such).

Also, after these hacks I would hope most companies will be considering adopting end-to-end email and chat encryption policies ASAP, to protect sensitive information (such as the dealings between Sony and MPAA) from getting out in such a leak - even if that means the top execs not having access to everyone's emails and chats anymore. Right now most companies prefer to spy on their employees, which makes them highly vulnerable to this type of leak in case of a hack. It also proves the point that surveillance is a bad "cybersecurity" policy (NSA and most other "security" agencies believe it's the solution to hacking, somehow). They might want to reconsider that and encrypt everything end-to-end.

They also need to compartmentalize a lot more. You can't have a "network of 50,000 computers" in a company, like I think Sony had.

I also believe it's already quite common for large corporations to have employees access the Internet only through a VM along with solid whitelisting policies (although I'm pretty sure Sony didn't do that and there are probably many more like them).

So yeah, I think the main point would be to keep security as close to an individual employee as possible, as opposed to having everything accessed company-wide, with virtually no protections within the network itself, just outside of it.