The Shulchan Aruch says that when puts on a new pair of tzitzis one should say birkat shechiyanu. I have heard that some don’t say Shechiyanu today because we are spoiled and not as excited over new clothes today as in the past. Should one still say a shechiyanu on tzitzis today?
With regard to a new Tallis Kotton, there is a difference of opinion amongst contemporary Poskim. Rav Zvi Pesach Frank (Har Tzvi Orach Chaim I:21) seem sto rule that one makes the Brocha. However, R’ Moshe Feinstein (Iggros Moshe, Orach Chaim III:80) rules that one does not say the brocha, because one makes Shehecheyanu only on an important garment. As such, someone for whom it is a significant acquisition may make the brocha but otherwise not (the fact that it is a mitzvah, says R’ Moshe, is not itself enough of a reason to justify a Brocha.
Yalkut Yosef (Orach Chaim 22) also rules that the custom is not to say Shehecheyanu on a Tallis Kotton.