Menchanko-Tei is a hidden, affordable little place on 55th that's great for solo eats. They have sushi if you've gotta have that, but their main attraction is the Menchanko soup. For less than $11, you get a huge cast-iron bowl of noodles and broth with all manner of seafood, veggies and such. Customize it with beef, pork, etc--it's a real plowman's meal and doesn't leave you stuffed. Don't be surprised if it's crowded at weird hours--the nearby banks' Asian-market staff takes lunch at night.