Times New Roman is the most common font for academic papers. Times New Roman has been a standard font for printers since the 1930s and this long reputation of readability has kept this font at the forefront of writing. This font is the expected font for any academic paper unless stated otherwise by the professor. Given its long history in the publishing world, it's probably a good bet for literary submissions as well.
Also called Arial or Calibri, this clean font is the standard of the design and marketing world. For a variety of complex reasons, the name of the font has changed throughout the years and there are certainly minor variations between Arial, Calibri and Helvetica, but they are all readable and clear fonts that are appropriate to use in any project.
According to the New York Times, this is the most popular font for websites. This font is clear and readable, but also has some character to it. This somewhat indefinable character seems to be what web content writers are responding to. Either way, if you're writing a blog or web article, Georgia is a good bet.
This font's predecessor, Courier, has recently fallen out of fashion. However, Courier New is the industry standard font for screenplays because of its clarity and readability. This font has a typewriter look to it, but is less compressed than its predecessor. So, if you're penning a screenplay or composing something for the film industry, Courier New is your best bet.