Of all the crazy and random additions I've made to bread doughs, semolina flour is the one that has become a regular component in my breads. It makes the bread a very pale yellow color and gives it a richer flavor. The first time I used it, it reminded me of a bread my mother used to buy from a local bakery when I was a kid, and that I hadn't tasted since.
Semolina is a course-ground flour made from durum wheat. I've also tried durum flour, which is ground finer, but honestly I didn't notice enough of a difference to prefer one over the other. Right now, semolina is easy to find, but I can only get durum by mail order. If both are available in your area, try both and see which you prefer, or just buy the one that's least expensive.