Command line is known to be the most powerful way of doing things on Linux. Even though there are GUI tools for almost any task, doing them in the shell is most of the time faster and easier. Not to mention there are so many CLI tools out there, you only have to build a graphical interface in order to use them. It is also the most common way of spreading tutorials or helping new users, since it's less bandwidth consumptive (no screenshots, no explanations like 'go there, click on that, not that, the one below it').
So, here are the most popular terminal emulators for X:
Konsole is the KDE terminal application. It can be configured in many ways, supports transparency (for desktop only), background images, encoding, pre-defined colour schemes (you can make custom ones), tabs (so you can have several sessions opened without the need to open another Konsole), and it's very rich regarding the configuration options.
This is GNOME's default terminal, and features desktop transparency and background images, encoding, profiles and more via the Edit -> Current Profile... configuration dialogue.
Yakuake is yet another terminal emulator for KDE. When I first started it, a notification balloon appears saying to press F12 in order to start it. Yakuake is always on top by default, but the nice thing is it disappears when you press again F12. So you can have a shell started all the time, which doesn't annoy you, use it on demand by calling it with F12 and then sending it back in the background.
You can configure Yakuake to change its size, be always on top or not, and you can disable the notification popup when it starts. Several more options are available.
XTerm is the smallest one, providing only a window with the size of 80x25. XTerm can be configured from command line. Though I rarely use it, I'll look into it and eventually post a how-to for those interested.
Eterm is yet another terminal emulator, with a futuristic theme. It integrates well if you are an eye-candy person, but otherwise, I recommend the use of a classic terminal. The thing about Eterm is that you'll have to launch it as Eterm from command line. That's right, the E is uppercase.
Some more terminals for X are Tilda, ROXTerm, rxvt, wterm. By the way, did you ever wonder what rxvt stands for? According to the official website, it's an acronym for our extended virtual terminal.
Updated: June 10, 2008 (Created: June 10, 2008)