If you're going to go with mint, definitely seek out peppermint (candy) and not spearmint (toothpaste).
The "mint" normally sold in grocery stores is spearmint.
The most obvious use of mint is in a chocolately stout, which is a good beer to experiment with and have on tap anyway:
Brew up a batch and keg (or bottle all but a gallon or two).
Soak peppermint in a bit of vodka for a few days.
When the beer is ready to drink, pour 3/4 of a pint, dose the peppermint tincture and swirl, taste, and repeat.
This way, if you really hate the mint in the stout, you still have all the base beer to play with other flavors (spices, cocoa nibs, fruit, etc.)