All you need is some paper or a blank journal if you want to keep all your tangles in one place. You can use a regular pen or pencil but Micron Pens ($12) are recommended since they're deeply pigmented, waterproof, dry quickly, and they come in different-size tips.
To make your Zentangle drawings appear more in depth, you can also use pencil and a tortillion, which is just a tightly rolled up piece of paper that helps smudge the pencil to create beautiful shadow effects.
You can also add color to your Zentangle drawings. I've experimented with using black ink over watercolor paintings. I've also used colored Sharpies and it just adds to the depth of creativity. I've seen people use white ink used on black paper as well, which creates a truly striking effect.
