The United States Postal Service has released their new Mark Twain stamp. It lasts 'forever' so you needn't worry about a price increase for this first class stamp. I love it and think I'll buy a sheet even though I don't use many stamps these days thanks to online bill pay.
You will enjoy seeing the other authors that have been honored around the world with their images on commemorative stamps in this article: Mark Twain and Beyond: Literary Stamp Collecting