Miniature Spotlights are the smallest spotlight generally available, it is only 39 mm across the face so it really is tiny!
They are an incandescent lamp so not energy saving and they only last for about 1000 hours. You can dim them.
They are also called R39 because of the size of the front of the lamp, this helps to identify it.
Not a lot else to say except consider trying the Halosaver version as it will save you a bit of energy!
Small screw (SES) base