I tried a Symbian touchscreen port of PuTTY/S60 the other day (can't remember if it's this one, or if there is only one (!)). It logged into my Synology NAS box with no trouble, though I was using my Apple Bluetooth keyboard rather than the onscreen one, which definitely helped - I guess the latter would be a real pain when it comes to SSH.
One thing that worked like a charm: if you use an HDMI display as a monitor, PuTTY can use the available screen space, so you can set the font size to a readable level.
Very handy app to have, if you ever need SSH on your S^3 phone. (Not that I often do, but... well, you never know ;-) )