After boots (my first buy) I go for Luden's Echo. However, is it worth rushing Luden's Echo on Kat at all?
Looking at the most updated pro-guide on Kat (http://www.lolking.net/guides/293542#items ) I noticed the lack of Luden's on there, which brings me to this question.
My current (Katarina) item set:
Core: Sorcerer's SHoes > Luden's Echo > Hextech Gunblade
Offensive: Zhonya's Hourglass > Rabadon's Deathcap > Void Staff > Abyssal Scepter
Defensive: Guardian Angel > Banshee's Veil > Rylai's Crystal Scepter > Lich Bane