Number 1 of "Ten things I love about Japan".
One has to begin here. Where else?
I can remember thinking, as a teenager in the eighties, how bizarre all of this raw-fish-and-seafood-eating was, and how exotic. Now having lived in Japan, it seems at once the most ordinary and the most indispensable thing. This is not to say that I routinely eat sushi or sashimi in Australia: I do have some standards. But then, I spend part of any given year in Japan, so I can afford to have standards.
Let's briefly get the terminology straight: sushi actually refers to the vinegared rice that is the base of the dish. Raw fish is only the most common of the toppings. Vegetables, seafood, cooked fish, cooked eel, and various other toppings are also used. And sashimi refers not only to slices of raw fish, but slices of raw flesh of any kind: chicken sashimi is extraordinary, although (I must stress) it's something I will only eat in Japan, in certain very good restaurants, in the company of culturally competent people whom I trust.
My typical sushi session begins with tamago (egg; in this case sweetened and scrambled) on sushi rice: even in Japan my habits are conservative. Then one of the mackerels: saba or sawara or aji or sanma. Then in no particular order a selection of hamachi (yellowtail) or kanpachi (a younger version), maguro (bluefin tuna), katsuo, iwashi (sardine), ebi (shrimp), and ika (squid). I go light on the last two, on account of my cholestorol, saving my ration for hotate (scallop), my preferred sushi-dessert. I'll toss in cooked unagi (freshwater eel) if I am in the mood. Soy as a dipping sauce, but not for unagi, which has its own special topping-sauce (similar to worcestershire), or for katsuo. The whole thing is helped along its way by pickled ginger as a palate-cleanser between sushi dishes, and generous quantities of green tea. Between these and the wasabi swiped onto the sushi rice, just underneath the topping, a sushi dinner doubles as an excellent herbal remedy against a cold ...
I am especially partial to katsuo. Wikipedia tells me that it's called skipjack tuna or bonito in English, and it may well be: but they mention nothing of its very particular, strong-but-not-overwhelming taste, or its texture. Texture is as much a feature of sushi and sashimi as taste, although I have no good vocabulary to describe it.
If you want to drink sake (rice wine) with the meal --- and I often do --- it's a better complement to sashimi. Sashimi can be served as an element of a multi-dish meal, or as a meal on its own: in both cases it comes garnished with shredded daikon, a white asian radish. When eating sashimi one has to add one's own wasabi --- not too much, people: it is not a contest! --- and if one adds it to the soy, there's the problem of keeping the daikon from soaking it all up: there seems to be some evil wasabi-daikon affinity. But I digress. My tastes in sashimi are similar to my tastes in sushi toppings, but with the addition of salmon (salmon sushi exists, but I am not a fan), and raw shrimp (likewise). And as for katsuo: you can get great huge inexpensive trays of the stuff at supermarkets --- its own special sauce included --- sometimes of a particular kind that's blackened just on the very outside layer, and still raw inside. I've no idea why it's so cheap.
If you do get trays of take-out sashimi from supermarkets, as I did a lot, you can wait until after local Japanese dinner-hour and get it at half-price: perfectly timed for the foreign researcher, cycling home from the lab. The quality is not as good as at a restaurant, but pretty good nonetheless: very good, by Australian standards. The same goes for sushi. As a take-out lunch, or for a dinner to take to duty-shift (eight hours staring at computer terminals underground: one gets hungry), I would often get a maguro plate: various tuna cuts including toro (more fatty), and various sushi types, like maki sushi (little rolls of sushi rice with nori [seaweed] wrapped around the rim, and a fish or vegetable core), and something similar but with the nori wrapping solid sushi rice, with minced raw fish on the top (I don't know the name). Trays with a full sushi selection are also sold; or trays of maki sushi, or some other type. One can also get inari sushi --- sushi rice stuffed into fried brown tofu --- although it's not my thing.
But the real deal is a restaurant meal: in my case (more by laziness than by other reason) it was often at conveyor sushi. It is a macho thing to be a sushi chef, and food-preparation-as-performance-art, still a relatively exotic thing for us Westerners, is part of the experience at a good kaiten-zushi house. Conveyor sushi is typically Japanese brilliance, by the way: fast food for the civilised.