Hamantaschen are a fairly ubiquitous offering in the many bakeries and delis in New York, and my first experience was with a raspberry jam-filled pastry the size of my hand on the Upper West Side. More traditional fillings might include sweetened ground poppy seeds, cream cheese, fruit compotes or dried fruit and nut mixtures, but there's almost never anything wrong with chocolate. The doughs one might use for hamantaschen are equally as various, from a tender shortcrust pastry, to a yeast or biscuit dough. What is always consistent, however, is the unique conical shape, always parted just enough to reveal a bit of what's inside.
UPDATE: evidently one reader found 1/8" to be too thin to hold in the filling. It worked fine for me, but this reader, before accusing me of disgracing the hamantaschen world (!!) suggests that you tend toward 1/2" to be on the safe side. I say, use your best judgment when rolling the dough out. If the sides seem too thin to hold the filling in, make them thicker.