iSSH is a wonderful SSH client that goes beyond a simple terminal client, to nearly the remote access Swiss army knife of SSH on the desktop.
SSH is commonly used as both a remote terminal and also as a sort of VPN to access remote systems graphically. Apple has limited the iPhone in such a way that this is impossible. A SSH connection can only be maintained in a single app, and when that app is closed, so is the SSH connection -- no other apps can access it.
iSSH gets around this by bundling in the two most common remote management systems: VNC and remote X11 applications. It also permits multiple simultaneous connections, so you can manage tasks between more than one server. (very useful in disaster recovery and server migrations)
As a terminal, iSSH is quite good. It supports custom fonts, different keymaps, copy and paste, and is in all ways a good solid terminal. Unlike other SSH apps, it also supports the legacy Telnet protocol and ANSI terminal emulation, in case you need to get your Tradewars on.
It also has a pretty easy way to get at non standard keys, such as arrows and modifier keys. A row of small buttons line the top of the screen, and you can scroll left and right to reveal more commands. This works all right, but I sometimes clicked the wrong key, even when scrolling, since the buttons are so small. This can be quite frustrating, and it made me miss TouchTerm's floating key palettes.
iSSH also has the option of a "key pie" menu. This brings up a floating round control that reminds me of a remote control for a TV. It can contain multiple sets of fully custom buttons that can be used as modifiers, macros, or arrow keys. I wouldn't mind seeing this concept completely replace the modifier keys at the top of the window.
VNC is well thought out and very flexible, thanks to the underlying SSH system for secure connections. You can connect in the clear, or using SSH tunneling, as well as tunneling to one server and then connecting openly to a second. Once connected, you have the normal sort of control, including window scaling, keyboard and mouse, and all the modifier keys you'd expect.
The winning feature here is the tunnel support. Performance over 3G is worse than some other VNC clients. Jaadu VNC can do the same SSH tricks and is generally a better VNC client, but it's also much more expensive. For lighter or infrequent remote management, iSSH is great, especially for the price. (note that VNC is perfect for remote control of presentations -- one more use for iSSH!)
X11 forwarding is very impressive, and quite a bit faster than SSH over slower connections (especially if you use something lighter weight than KDE or Gnome) But it's limited to pure Unix systems, and more complex to set up than VNC, so it's only a real benefit to the most die hard *nixers. That said, it works great, up until you run out of memory. (Which, on my 3G, was after just a couple of KDE apps -- a 3GS would fare better)
The one limit on remote management is that only one graphical (VNC or X11) session can be active at once, although any number of terminals can run at once. (until you run out of memory, at least)
To wrap up, iSSH is fantastic. It gives you all the tools you need to remotely manage Unixish servers from your phone. (Windows, too, if you install the right open source tools) It might be just the thing to let a IT professional take a vacation without needing to drag along a laptop and stay near wifi in case disaster strikes at the datacenter. Or, for $5, it's also just a handy tool for any *nix hobbyist.
