According to fonts.com and fontshop.com the following fonts were best sellers in 2009:

Arial •  ITC Franklin Gothic • Benton Sans • FF Meta • FF Din • Eurostile •  Gill Sans • DIN Next • Avenir • Futura • Frutiger • Helvetica • Interstate • Akzidenz Grotesk • Univers • Trade Gothic • the Sans • Neo • SoHo •  ITC Avant Garde Gothic • Rotis • Zapfino • Optima • Estillo • Helvetica Neue • Estilo Script • Waza™ • Olicana Smooth OT • Louisiana • Metroscript OT

There are many more classic fonts than I would have imagined.

If you haven't visited fontshop.com lately, you have to check out their new tool: type navigator, it helps you figure out what type you need by the specific characteristics of a font. You choose the size of the serif, the general shape, proportions, weight and more, of the characters you want and it matches your choices up with all of the fonts within close match of those characteristics. It's just another way to search for a font when you're not sure what you're looking for, or if you know what you want it to look like, but have no idea what the name of it is.