Hmm I have a paper on SSH lying in my library, I'll upload it for you and give you a link in a couple of days.
Stunnel basically allows you to wrap any service in SSL encryption. Basically if you have non encryption aware daemons running then you can use Stunnel to wrap the session in SSL. A very useful implementation is to lock down your POP3 email access, POP3 sends passwords in cleartext, so stunneling the POP3 daemon would be a good way to work around that. Another use is to run stunnel over ppp for a sort of makeshift VPN.
Theres lots of info on the net, I'll give you a couple of links