I would TOTALLY be into into custom designed halters. They sell these REALLY awesome dog and cat collars at the vet clinic around the corner. They are a very durable cotton, triple or double stitched, and made with really neat patterns or textures. I have been REALLY wanting something like that for my horse. And, you could do a 'halter bridal' with matching reins and or lead ropes as well as a matching pad (just get a regular pad and use fabric glue and a sewing machine)
You can do the same thing with super cheap halters and just glue and sew (both, not one or the other) the more interesting patterned fabric over it that could also go on nylon tack accessories like breast collars and so on.
You can also make little strands of beads with a clasp that people can put on their saddles, halters, bridals or key rings. Add a tiny rubber band and you have a strand of nifty main or tail beads!!! (Hmmm...thinking of this makes me want to do it!) I'm not just talking about those cheezy plastic beads though, I'm talking about the nicer glass, wood, or 'decorative' type beads.
Or, you can totally 'bedazzle' blankets and halters with horse's names, breeds or even "I love my rider" kind of stuff
I'm a crafty and artistic person and have been thinking of doing something similar, but I never do...I'm such a chicken lol