cPanel, InterWorx, DirectAdmin and Plesk are the popular ones.I will prioritize the control panels as:
From Administrator point of view:
1. cPanel
2. InterWorx
3. DirectAdmin
4. Plesk
From End user point of view:
1. cPanel
2. InterWorx
3. Plesk
4. DirectAdmin
cPanel is the first choice if you want to have a complete hosting panel. I would say that "cPanel is not just a control-panel, but a complete server setup".
It provides alot of features for the users to manage their websites and the servers. For administration point of view it provides scripts that can be used to fix/upgrade installed applications.It provides a clean setup and you don't have to rely on cPanel. Most of the applications can be upgraded easily.
The first thing that I like about InterWorx is its cool interface . From end user perspective, it provides limited features but that are almost enough to manage the websites.It is not resource hungry and a light control panel. For administration point of view, it is also easy to manage, fix and upgrade the installed applications.
Directadmin is a very light control panel with very limited features. If you don't need much features and need a simple control panel that can run your websites then go for it. Its three access levels are somewhat confusing at start.From administration point of view, it also provides few scripts and the installed applications are easy to upgrade.
Last but not the least Plesk, it provides a cool interface to the end user and is a light control panel. It is easy to manage for end users and the interface is quite easy to use. But installations/up gradations of installed applications are quite complicated in it and really sometimes it will give a tough time to upgrade any installed application. Mostly you have to rely on Parallels that when they officially support the latest version so that it can be installed on it.