It seems to me based on these two fairly reliable opinions [here][1] and [here][2] that the proper barakha for most sushi is mezuznot.  

Though if you have some of the more interesting varieties of sushi that are lacking the rice and comprise other things it will probably need to corrected accordingly.

  [1]: http://www.yeshiva.org.il/ask/eng/?id=780
  [2]: http://www.thelakewoodscoop.com/news/2010/02/reb-simcha-bunim-cohen-shlita-picks-up-sushi-and-puts-it-down.html