Current female ruler topless: wow! (7)
I believe the answer is:
impress
'wow' is the definition.
(I know that wow is a more specific form of surprise)
'current female ruler topless' is the wordplay.
'current' becomes 'I' (symbol for electric current).
'female ruler' becomes 'empress' (female version of emperor).
'topless' means to remove the first letter.
'empress' with its first letter removed is 'mpress'.
'i'+'mpress'='IMPRESS'
(Other definitions for impress that I've seen before include "Simpers so as to make mark" , "gain effect" , "Use stamp; earn respect from (someone)" , "Influence - conscript - stamp" , "Earn good opinion of, or stamp" .)