Any working ssh client should be able to connect to our systems. The "reference" implementation in our opinion is the OpenSSH application, available on most Unix platforms (including MacOS X, most easily accessed using the included "Terminal" application) and on Windows via the Cygwin or Interix environments.
On Windows, the far-and-away best ssh application is VanDyke Technologies' Secure CRT. This program is rather expensive ($99) but worth every penny if ssh on Windows is a part of your daily life. PuTTY is a very popular free alternative. It is a little less pleasant to use, but is very workable. (PuTTY requires no local installation and is a perfect tool to slap on a USB memory stick for secure access from anywhere.)
Other alternatives do exist, but these are the most common and the ones we use ourselves.