PuTTY and GSSAPI
I had been using a version of PuTTY with GSSAPI extensions for quite a while and it seemed to work well. That is, until I tried to set up Kerberos on a new Debian VPS. That version of OpenSSH apparently has issues with the PuTTY client I had been using.
After much trouble, and trying multiple clients, many of which did not work with MIT Kerberos for Windows, I found Matthew Loar's PuTTY GSSAPI. Worked like a charm. Check it out.