A Quake-style terminal is a drop-down terminal which can be shown/hidden just like the console in Quake (and most of the first-person shooter games out there), using the press of a key (~ in Quake). Guake is a terminal application written in GTK which uses the F12 keyboard shortcut by default to show or hide it.
Guake - drop-down console for the GNOME desktop environment
Guake features transparency, tabs, tray icon, configurable shortcuts, fullscreen mode and allows you to change terminal size, transparency level, appearance, font size and default shell interpreter.
Terminator - feature-rich terminal emulator
Terminator is a powerful terminal application written in Java with support for features like tabs, automatic logging, text drag & drop support, find function, split the current tab horizontally or vertically, profiles, appearance settings (transparency and background image, colours), plugins and configurable keyboard shortcuts. All in all, Terminator is one of the most powerful terminal emulators out there.
With features that make it unique, Terminator is a must-try
Konsole - KDE default terminal
Being the default terminal for the K Desktop Environment, Konsole brings usual features like transparency, profiles, notifications, shortcuts, tabs, appearance configuration, but also bookmarks, monitor for silence or activity.
Powerful enough, Konsole usually fits most KDE users who need a terminal to blend into the environment
Yakuake - Quake-style terminal for KDE
Yakuake is the terminal of choice for those who use KDE and like the Quake-style approach. Triggered by F12, Yakuake supports tabs, profiles, transparency, resizing, colour and font size configuration, active tab splitting. A very good alternative to Konsole.
Yakuake - drop-down terminal for KDE
GNOME Terminal - GNOME default terminal
GNOME Terminal ships by default with the GNOME desktop environment and it features profiles, configurable keyboard shortcuts, tabs, fullscreen mode, find function, transparency effects, background image.
The default GNOME terminal application
GNOME Terminal allows to configure a profile and change appearance settings (including transparency level, background image, colour scheme or terminal fonts), scrollbar, bell and terminal size.
Tilda - Another Quake-style terminal
Tilda is yet another powerful Quake-style terminal written in GTK which uses by default the F1 keyboard shortcut to show/hide it. It features tabs, transparency effects, build-in text and background color schemes, and powerful configuration options. When first started, Tilda will show the configuration window, where you can change behaviour like showing it on taskbar or start it hidden, change the title and the default web browser to open links, change size, position, enable transparency, choose background image and enable animated pulldown, colour schemes, enable/disable thescrollbar, compatibility options and show/hide keybinding (default F1). The animated pulldown looks kind of ugly though (GNOME 2.32 and Tilda 0.9.6). It doesn't seem to include support for changing the console font, maybe I missed it? Otherwise than that, Tilda is a very good alternative to the ones already mentioned.
Tilda - an alternative drop-down terminal for GNOME users