Must Have One or More: Audio Technica AT95E Cartridge
I kid you not, when properly set up and paired with a quality MM phono stage (e.g. an iFi iPhono2 with iPower Elite), this ~USD$50 cartridge sounds so airy and supple, much like a Koetsu or high-end ZYX. Every vinylphile should get at least one of those into her/his system to see how a cheap cartridge can, in almost every thinkable sonic category, perform better than a lot of super expensive ones. I do have several >USD$10k cartridges for reference, BTW.