For us it has to be Kilrock descaler gel. It even comes with a small brush! Wipe it around tricky places, such as a shower head or the tip of a tap, leave it for some minutes et voila! magic! no more limescale.
It is OK to use on stainless steel, plastic and ceramic, but be careful with enamel.
Try it and let us know what you think or share with us your best ever cleaning product!