How can I descale my kettle safely?

Which products can I use to descale my kettle safely? (Products available in the US please.)
Arnold, February 2004


done
Usually ordinary vinegar will do the trick. Just let it soak and you will see the scale bubble off.

Tom, October 2007
I just boiled a full kettle with a tablespoon of white vinegar for five minutes and it got all the residue off the bottom of the kettle. I rinsed it thoroughly and let it air dry to get rid of all the vinegar taste and smell.

Shayla, April 2007
Do you remember the old fashion TANG. It works but its called orange crystals now. Put half package to full kettle of water, keep lid up so that kettle can continue to boil for 2 mins. Boil kettle with clean water a couple of times to get rid of the orange taste. Wipe out any scum or residue with paper towel.If your kettle is plastic inside it may discolour from the orange colour but it remains safe to use

Lorraine Thistle, June 2005
Cut a lemon into quarters and pop them into the kettle. Boil kettle once or twice then remove lemon pieces. Wipe off residual lime in kettle with a paper towel; Simple and Safe.

Jim Lindsay, May 2004
I'm told that white vinegar (diluted with water) left in the kettle over night should remove limescale.

terry mcauliffe, May 2004