His first tattoo was "Japanese Zombie Heroez" on his right arm, he got it in late 2002.
He also has a cross on his right middle finger, "Despair of the Fault" written on his left hand, a blue fireball on his right hand, between thumb and forefinger, got a spiderweb on his left arm, along with a few ghosts...
On his neck, there is a bat-shaped tattoo (not sure on this though).
Kaoru had his whole right arm tattooed recently, got a couple of motives on his whole right arm, along with a tattoo on his knuckles with Russian letters, but I don't know what it means yet (or if it's really Russian XD) =>see last pictures.

At first, Kyo didn't have many tattoos, but as time passed, more and more images appeared on his body. When Kyo started with Dir en grey, he only had a butterfly on his right shoulder, then a dragon appeared on his left arm, later he decided to have a non-figurative background to the butterfly, along with a Russian word родиться (to be born) below it - altough now it can't be seen, since he has a thick non-figurative wires tattooed around the butterfly, which overlaps the writings.
His obsession with the Russian culture didn't expire there, he has a crown (that resembles the Crown of the Russian Empire), on his lower arm, with a five-pointed star and the Russian words in order are:
вечный (Eternal),
сон   ум (sleep   mind),
счастье (Happiness),
свобода (Freedom)
- these are still visible. He also has Russian words on his fingers: боль (Pain), and бог (God), he got them in late 2001.
In late 2005, he got a cross on his finger (like Kaoru). In late 2006 - during the Family Values Tour -, he got "Damned" tattooed on the left side of his neck.
He has "The Emperor Is Dead" on his right hand, a crowned skull below his right ear, also a skull on his right shoulder (which he got recently). He also has a man's face above the russian crown.
He got a black tiger in red flames on his left hip in early 2008.
As Kayle pointed it out: The cross on his middle finger on his right hand got covered up recently, and it looks like he had the skulls on his knuckles touched up some.