Drop D is quite good for doing some slide too, just get a bottle neck (if you can get one, find something metal/glass, smooth and curved), and slide it up and down the strings why playing the D (which was an E before it was tuned down) A D strings, (the thick three strings).
Just touch the strings, dont press them down. Hover the bottel neck over the frets while touching the strings, and shake it a little bit... this sounds pretty cool...