Coffee stain in coffee cups I've noticed that my coffee cups are getting stained.  Neither myself nor the dishwasher can get the stains out.  Any suggestions? (Other than buying new cups ;)
Baking soda. I use a standard dish sponge/scrubbie with baking soda and a little water and it comes completely out. I've actually tried it with just a damp paper towel and baking soda and it's almost as easy.

Baking soda has natural whitening properties and is a very gentle abrasive. I actually started using it elsewhere (sinks, counter tops, greasy pans) before discovering its use in coffee cups.

I've also tried baking soda + salt on counter tops and pans with great success. Salt has similar whitening properties (surprisingly to me) and is a stronger abrasive. Haven't tried it in coffee cups, but you might consider trying that if you need a little extra cleaning power. (Also: Aside from being cheap, baking soda / salt are food-grade and non-toxic!)