Konsole: This is a powerful and full-featured terminal included by default in KDE. It features desktop transparency, background images, profiles, tabs, notifications and plenty schemes to choose from.
GNOME-Terminal: The GNOME terminal, it has support for tabs and desktop transparency, with a clean and simple interface.
Yakuake: A wonderful terminal application for KDE which has the big advantage to stay hidden unless called with F12. It has a style similar with the Quake 3 console or other FPS games. It can use Konsole's settings, including transparency effects and notifications.
Tilda: Tilda is yet another terminal which has a style similar to Quake consoles. I could say it's the GNOME counterpart to Yakuake. When you first start it, you'll be presented with a window to configure it and choose the global shortcut for showing/hiding it.
ROXTerm: ROXTerm is a GTK terminal application with an interface similar to the one of GNOME-Terminal, supporting backgrounds, desktop transparency effects, profiles, colour schemes and many more.
xterm: xterm is the tradition terminal emulator for the X Window System, with a minimal interface. It can be configured using its configuration file.
Eterm: Eterm is a terminal with a futuristic design similar with Enlightenment styles. You will have to run it as Eterm, with capitalised E.
xvt: This is a basic terminal which uses a very small amount of memory, similar to xterm in many ways.
rxvt: It stands for our extended virtual terminal, and it's intended to be a smaller replacement to xterm.
mrxvt: Mrxvt supports tabs and background images while not being memory hungry and not depending on KDE or GNOME libraries.
rxvt-unicode: It features transparency effects, it has scrollbars and support for Unicode characters.
aterm: The AfterStep xvt terminal, aterm is based on xvt and needs less memory than xterm.
wterm: Another lightweight and simplistic terminal emulator which includes scrollbars, background images and transparency.