in one of my more formal gardens, I used brick walkways between beds. It's pretty, but high maintenance (weeding) and not very comfortable to kneel on. My favorite walkways are those I planted in wooly thyme. It took some work to get a good, weed-free base, and it took time to fill in nicely, but now that it's established, it's pretty carefree (a thick, weed-smothering mat) and it's easy on the knees and feet, and it smells great to walk and kneel on. The seed was a little pricey, but I haven't had to do anything with it for years, so in the long run, it might be cheaper and easier than mulches that have to be replaced.
By the way, there are many different types of thyme...I chose wooly because it stays very short, but almost any of them take some foot traffic and grow pretty easily (although slowly) from seed.