Twitcher

The Twitcher is a task switcher to jump between running applications and their windows.

twitcher.png

Hold CTRL and tap TAB to switch between the current and the last application/window on the current workspace. Tapping TAB very quickly will switch between all visible applications on the current workspace.
Press and hold CTRL TAB to open the Twitcher window and go through all running applications by repeatedly hitting TAB or /.
If you need to get to a specific window of a program, move to its icon as described and then go through its open windows with the / keys.

You cycle through all visible windows (on the current workspace) of an application with CTRL ~ (which, depending on the keymap you're using, is the key below ESC).

It's also possible to invoke the Twitcher with CTRL TAB and then use the mouse to choose the application/window you'll jump to when releasing the CTRL key.

The Twitcher also offers a few more advanced keyboard shortcuts:

ESCAborts the twitching and returns to the formerly active window.
QQuits the selected application.
HHides all windows of the selected application.