I recommend a Epipremnum, it grows fast and gets long but since it's a single vine with leaves it's also ideal to guide it along branches... Another plus is that it's easy to multiply it by making cuttings.
Also a good one to have is the schefflera, they come densely bushed which offers good hiding places for your chameleon, just make sure they are slightly elevated offf the floor and the pot has a hole in it for proper drainage or it will likely get root rot and die off.
If you're looking to add some color to the enclosure the bromelia is a good go to plant, it doesn't offer much climbing possibilities or cover even but the flower is pretty and lasts very long. Maybe not so good to have in smaller enclosures but if you have an open spot to fill in it has a lot of decorative value.
The ficus benjamina is also often recommended but in my experience it loses a lot of leaves, tends to grow trough the mesh and has a sticky milky substance comming out of broken twigs and leaves. It also has a milky substance coming out of leaves/twigs that are cut/broken which is midly toxic and can cause some inconvenience for your veiled (should be nothing leathal) or to you if you're alergic.
Someone should make better work of this page:
https://www.chameleonforums.com/care/plants/