I always buy a packet of citric acid in the chemist or wine making shop and use that to descale my kettle. Mine is one of those glass ones, so I have to do it regularly to keep it looking good.
my mother-in-law gave us a new kettle 3 yrs ago and put some sea-shells in it. i thought she was mad but somehow the shells have stopped the kettle from getting limescale, which is very easy to get round here as the water is very hard....try it, just 2 sea shells n leave em in the bottom of the kettle.