Every 6 months or so (looks like I waited longer in this photo) I pull out all our well-used coffee mugs and bleach them in water to get that nice, new look again.
Just fill up a tub or your sink with about 1/4 cup of bleach and water. Put in about 6 mugs at a time and let them soak. I had to wipe a few of them with a microfiber dish cloth but they cleaned up great.
You could wash them afterwards (to get the bleach smell off) by hand but since the dishwasher was empty, I loaded it up with all the mugs. I even did our Christmas mugs that were in the china cabinet so they're now ready for the holidays.
Voila! Clean coffee mugs again! Take a look at your own mugs and cups and try this little "treatment". I'm having ladies over tomorrow and Friday so I wanted to spruce them up a bit. :)