iznenađivati

1. (+ acc.) to surprise; to astonish
   Ona me stalno iznenađuje svojim idejama. — She keeps surprising me with her ideas.
   Ne iznenađuje me što kasni. — It doesn't surprise me that he's late.
2. (iznenađivati se) to be surprised; to marvel
   Stalno se iznenađujem koliko je grad porastao. — I'm always surprised by how much the city has grown.

The perfective is iznenaditi; iznenađivati se usually takes the dative or a "što" clause.