We have a rule: Thou shalt never allow unencrypted log-ins. This means regular old telnet is out, and SSH (Secure Shell) is in. Zinger-Soft’s iSSH has just about everything I need to work on a *NIX machine, combining support for a wide variety of terminal emulations (VT100, VT102, VT220, ANSI, and xterm) with a tunneled VNC client, RDP, and x-server. Heck, you can even do a key exchange for public-key/private-key authentication. Maybe a bit expensive for an iPad app, but it’s a full set of features for $9.99.
Compatibility: iPhone and iPad; iOS 3.2 or later