Anyone know what software I could use to create expandable encrypted
file containers?

TrueCrypt is wonderful... but you can't resize the encrypted files it creates.

Aka - I want to be able to mount a file as an encrypted file system,
copy arbitrary files into that file system, unmount it, and copy the
file containing the encrypted file system to another server where
there is no security.

But I don't want to have to know the file size ahead of time - which
TrueCrypt requires.

Thanks,

Dan