Very popular free SSH client. Connects to hosts via secure shell, telnet or RS232. This program has been around for ages. It may not be the prettiest one, but it does the job and it is free.
Ranked in these QuestionsQuestion Ranking
Pro De facto standard client for SSH, Telnet and Rlogin
PuTTY is one of the oldest and most popular clients. It has earned the trust of a great number of users over a long period by being reliable, offering useful features and helpful support. It got into the 15 Essential Open Source Tools for Windows Admins list by InfoWorld.
Pro Can be used on any Windows computer, even without admin rights
Pro Source code available
Full source available. Compile and modify it yourself.
Pro Lightweight and portable
Doesn't require much resources (memory and hard-disk). Can even be run on a system by just downloading without install.
Con Can not save passwords
Anyway, you can use "PuTTYgen" to generate a key pair, then use "Pageant" to do a password-less SSH remote login.
Con Lacks features
It is JUST an SSH client. There are many other options with built in X-servers, Multitabbing, etc.
Con Ugly design, too simple
Looks very dated. Does the basic functions very well, but not much more.
Con No global settings
If you want to change a setting for all your connections, you'd have to do it individually.
Con Organizing sessions
Does not have features for organizing session connections (like folders). If you have 5-10 connections that's fine. But if there are 30-50 connections - that becomes a nightmare.
Con Only one session
Cannot open a second session in the same window.
Con Tedious logging/tracing
Its tedious to set up logging and tracing (e.g. for serial connections).