Zytel is a trade name used by DuPont for fiber reinforced Nylon, also known as FRN.
Spyderco has a lot of FRN handles.
So does Cold Steel.
Benchmade does also in some of their lines.
G10 and Micarta are grippier. Since they are machined, rather than molded, they are less expensive for short runs. FRN must be compression molded and the dies are very expensive. FRN is less expensive only if you are making a lot of knives with exactly the same handle shape (which allows you to use the same set of dies rather than making a new set at ~$40K per set.)