I have a collection of thermal coffee mugs that I use to drink my coffee on the road that I have collected over the years. Some have been free promotional mugs and other that I have bought. The best ones that I have found to fully enjoy your coffee are the ones with a stainless steel interior. The plastic interior on the most cups tend to leave a plastic taste to your coffee but the steel ones let you enjoy the full gourmet coffee flavor. I finally found a particular thermal coffee mug at Costco one day that has turned out to be the best one that I have ever used. It is made by Contigo and it has a solid top that seals in the heat with no spills.
It has a clip in the handle that you can use to attach to your book or lunch bag without worrying if it is going to spill. Since Costco does not currently carry the mug you will need to find an available retailer at Contigo.com.
I did have a problem with the pair that I bought in that the flip top levers both broke after a few months. I emailed the company and they gladly replaced the tops at no charge. A great coffee mug with great customer service that stand behind their product.