When I got my iPhone about 9 months the one app I wished for was a terminal. I wanted somthing to enable me to quickly login to my servers and fix problems when in work and stuck behind a proxy or when away from the desk.
There was first a web app which turned out to be a joke, luckily I had that thought and tried it with bogus details. Then there was a homebrew app, but I failed at jailbreaking my iPhone. Then there was another web app, but this time hosted on your own server. This took a little bit of fiddling and messing about to get setup, and was a little clunky, but did do the job.