Black light is great, but, if you don't have anything under it that can glow, what fun is that? You gotta place items that are black light sensitive under the black light in order to make that area of your Halloween yard haunt or cemetery that much more fun and mysterious.
There are plenty of Halloween props and decorations out there that are black light sensitive that you can buy and place around your home or yard. The cheapest among them being the stretch-and-pull spider webbing. While we're not real big fans of this item, to its credit it glows fantastically under black light.
But, what if you've already got a large collection of your own Halloween props and decorations that don't glow. What do you do then? Enter glow-in-the-dark paints and pigments. There are dozens of different types, brands, and places to buy them to suit just about anyone's specific needs.
The most basic, of course, is GITD spray paint. You can get this at just about any hardware store and it's relatively cheap. It'll work great on wood, metal, and even clothing, but not so well on plastics. It does have a tendency to peal and flake on smoother surfaces.
Next, there are liquid GITD paints you can brush onto just about any surface. They are available in latex and acrylic. These come in a variety of colors and are available at most hardware and hobby/craft stores. And, they too are relatively inexpensive. Small 2 oz. bottles available at craft/hobby stores are great for adding some GITD accents to your existing props. For example, if you've got a latex cat, you can paint its eyes, teeth, and claws to make them glow in the dark.
Last, there are GITD pigments which you can then add to any clear/translucent non-water-based paint or lacquer. I've linked an example, but there are plenty out there and they're relatively easy to find on the internet. They are relatively expensive, so make sure you know exactly how much you need so you don't over-buy.