Salmon
Salmon is an extremely popular fish for both sashimi and nigiri partly because it doesn't have the strong "fishy" taste that many people fear. Easily distinguished by its peachy orange color, salmon's smooth flavor makes it a safe, non-threatening choice for sushi beginners.
Tuna
Bluefin tuna is perhaps the most common sushi fish, so much so that it is classified as an endangered species due to overfishing. This fish actually yields different cuts of fish for sushi. The cheapest and most common, akami, is the leanest part of the fish and has a metallic fishy taste. This is the dark pinkish-red meat that you typically see in sushi rolls.
The most prized cut from the bluefin is called toro, or fatty tuna, which comes from near the belly of the fish. Otoro has a lighter pinkish color and a richer, fishier flavor than akami does. As the fattiest part of the tuna, this cut is known for being so creamy that it falls apart and melts in your mouth like butter.
Eel
Unagi, or freshwater eel, is most commonly served grilled with a sweet, teriyaki-like brown sauce known as unagi sauce. The sauce generally masks any eel-like flavor, which makes this a comfortable choice for sushi first-timers who aren't quite ready to try raw seafood yet.
Nearly every sushi restaurant receives unagi prepackaged and pre-seasoned, making it fairly consistent from restaurant to restaurant.
Yellowtail
Also known as hamachi, this fish has a delicate savory flavor. Its high fat content also gives it a creamy, buttery texture, which makes it a popular choice for nigiri. Its color can vary, but it should generally be a light, opaque pink with a brownish tint.
Flying Fish Eggs
Known in Japanese as tobiko, this fish roe comes in a variety of colors but is orange in its plain form. The small eggs have a smoky/salty taste and a peculiarly crunchy texture that, combined with its appearance, may be intimidating to the less daring.
Sea Urchin
While sea urchin or uni isn't exactly a sushi fish, it's such a well-known delicacy in the sushi world that it can't be excluded.
Uni is famous for being either loved or hated. It's often described by its fans as tasting like the ocean without tasting fishy. However, while it's seen as exotic and almost universally praised by food critics and chefs, many people are put off by its appearance, texture, and taste.
Fresh uni should look firm, not slimy, and it should have a creamy, melt-on-your-tongue texture. Ranging in color from gold to light yellow, it has a light, sweet, ocean-y flavor that makes it a rare treat and must-try for adventurous sushi eaters.