Best Multi-OS AuthN Solution?

Dear Lazyweb,

I'm going to be building a heterogenous network consisting of Linux workstations and servers, Mac workstations and laptops, Windows desktops and laptops (maybe the odd server here or there), and maybe a few fringe operating systems. It's completely Legacy Free: nothing there at all. My goals are to make sure that all my various CIFS/NFS/AFS shares are sharing credentials just fine, and that users don't have to maintain multiple passwords.

What's the current vogue for this? Ideally I'd be running something on !Windows, but if I need to stick a Windows Server somewhere I'll do it. I'd rather not, but I will. If not ActiveDirectory, do I roll with LDAP? Which implementation? On which OS? Do I go with kerberos, or the LDAP/NIS for *nix logins? Remote/semi-connected users?

I can't believe I have to ask, but working for Big Companies has addled my Systems Administration skills slightly.

Thanks in advance,
Kirk

P.S. I tried to ask this in ServerFault and before I could add content it warned me that the question was subjective and likely to be closed. So I didn't bother.