The only thing you really need to do latte art is milk, and you need some espresso to pour into, of course, and a pitcher to pour with. For free pour you don't always need a pitcher with a spout, but it really helps if you want to be manipulating the lines or creating ripples.
A spout is a really great thing to have. Although if you don't have one, you can still do things like monk's heads, or solid-shaped hearts and do some very basic rosetta-type things. But yes, for most free-pour latte art, you want a pitcher with a spout. You need espresso to pour into, and of course, milk to pour with. If you're doing etching or any sort of garnish, then you might want to be using some syrup for that or a chocolate powder, and then use some sort of pointy object.
You can either use a thermometer, which barista's usually have one around or really anything pointy. We have a screwdriver and an awl here. A toothpick, anything that you can use to paint or drag syrup or dots around the cup is just fine. That's everything you need to pour latte art.