You don't need fancy dice to play a tabletop RPG, and contrary to popular superstition fancier and more expensive dice don't roll more successful saving throws and critical hits.
However, some gamers just enjoy spending money on their obsession, and their gaming kit doesn't feel complete without some shiny and expensive dice, so their group will see them rollin' and get super jealous.
But if you're looking for dice that will both make your group jealous and make it impossible for them to tell what you rolled take a note from this Dork Tower comic by John Kovalic and grab some Elvish Dice of Inscrutability!
-Via Geeks Are Sexy