Slide
Edge uses a brass slide. Check out the Boston DVD, you can see him using the slide on Kite. Something very unconventional that Edge does (along with the rest of his "unconventional" approach to guitar playing) is that he uses the slide on his middle finger, rather than on his ring finger as you see most players do. Kinda odd, but it works for him and it is easier to switch from chords to slide with it on your middle finger.