From http://shfs.sourceforge.net

Shfs is a simple and easy to use Linux kernel module which allows you to mount remote filesystems using a plain shell (ssh) connection. When using shfs, you can access all remote files just like the local ones, only the access is governed through the transport security of ssh.

Update – 2006-12-21: These days I use FUSE/sshfs, which does the same thing, and does it in userspace.