1) Central's lobster and tuna burgers
The most celebrated crustacean-based burger in Washington is undoubtably the $30 brioche-bun-ensconced lobster burger at Central--made with tail meat bound together with scallop mousse. It's just one of those must-eat DC dishes. The ahi tuna burger--a relative bargain at $20--is an ocean-sourced sandwich that gets less buzz, but is also really good. Both come with the restaurant's perfectly crisped fries, and are exactly the right thing for a solo dinner at the bar or a mellow Friday afternoon lunch with friends.
2) The mussel burger at Et Voila!
Some people see the mussel burger at this MacArthur Boulevard Belgian restaurant as a mere novelty item. I mean, a burger made out of mussels? Is that for real? It comes down to personal preference. If you love the briny taste and chewy quality of bearded bivalves, you'll likely enjoy the briny taste and chewy texture of the sandwich. But no matter how you feel about mussels, you should try it--at the very least, it makes for a fun barroom brag. The aïoli-drenched moules burg is $15.95--other maritime burgers at Et Voila! include shrimp (with shrimp mousse, also $15.95) and lobster (with lobster mousse, $18) sandwiches. The last may not rival Central's for richness and girth, but it's still pretty tasty--not to mention $12 less.
3) The fish sandwich at Westend Bistro
Eric Ripert's window-lined restaurant in the Ritz has had its ups and down, but the fish sandwich remains a beloved mainstay on the menu. The patty's crisp exterior surrounds a just-soft-enough, just-oceany-enough center. A generous smear of saffron aïoli adds bright flavor. It's $16.