Love the Naschmarkt! There you find stuff you cannot get anywhere else! My favorite place is the Palatschinkenkuchl - they serve all kinds of crepes, from sweet to savory, among the sweet is one laced with Mozart Liqueur , and now that asparagus from the Marchfeld is in season, a Asparagus and Ham Crepe is heavenly!
If you are a early riser, then the Fleamarket on Saturday is a treasure trove - but the good stuff is mostly gone long before noon.