Cooler weather seems fitting for hot chocolate. You may make fancier drinks at home, but if you want hot chocolate while at work, you are probably looking at a mix of some kind. I have tried lots of them.
One way to make all of them better is to make sure you don't add too much water. Most of the packages are set up for six ounces, not a full-sized coffee mug. If you fill the cup with eight or more ounces of hot water, the mix will be too weak, and you may be inclined to blame the manufacturer. Keep the water to six ounces for a thick cup of chocolate.
As for the mix, I like the Nestle's Hot Cocoa Mix. It is "subtitled" "Rich Chocolate Flavor." It comes in a 0.71 ounce package. Office Depot sells it. I have not seen it in stores. It seems to work best when all you have is hot water. Of course, heated milk always improves a hot cocoa mix.
Give the Nestle's Rich Chocolate Flavor Hot Cocoa Mix a try. It is fairly inexpensive, and has a true hot cocoa taste.