For all the coffee lovers out there, nothing is more frustrating than a lukewarm sip of what was once a piping hot cup of joe. Enter the coffee mug warmer – your BFF for keeping every cup at the perfect temperature. Coffee mug warmers are so handy, whether you're deep into the workday or relaxing with a good book during the weekend. There are so many to choose from, and these 7 top-rated warmers ensure your brew stays warm to the very last drop.Cafzed Coffee WarmerThis $22 (was $24) coffee mu...