My mate at work is mad about fatty Tuna (I think it's called 'Toro')
I've only got into Sushi and Sashimi fairly recently.
It used to scare me but now I love it. I like Tataki sushi - it is seared along the edges.
One of the things I really like about sushi is the accompanying stuff like Wasabi and pickled ginger. The Japanese have some amazing pickles - they put to shame the sorry-looking pickled eggs you see in UK Fish & Chip shops.
I've yet to try Japanese steak but I heard it's really good.
Recently I went to a sushi bar with the guy from work, and we had 'the membrane that contains a sea scallops internal organs', as a freebie because he knows the owner.
It was nice, although the chef didn't tell us what it was until after we ate it!