Via Wikipedia:
A Sparkline is a type of information graphic characterized by its small size and data density. Sparklines present trends and variations associated with some measurement, such as average temperature or stock market activity, in a simple and condensed way. Several sparklines are often used together as elements of a small multiple.
The term ‘Sparkline’ was proposed by Edward Tufte for “small, high resolution graphics embedded in a context of words, numbers, images.” Tufte describes sparklines as “data-intense, design-simple, word-sized graphics”.[1] Whereas the typical chart is designed to show as much data as possible, and is set off from the flow of text, sparklines are intended to be succinct, memorable, and located where they are discussed.
On November 12, 2009, a patent application was published [2] which had been filed May 7, 2008 by Microsoft employees, claiming various aspects of Sparklines’ implementation in Excel 2010, prompting Edward Tufte, the acknowledged inventor[3] of the graphic, to express concern.[4]
Google Docs has sparkline support. There’s a free, third-party plug-in for adding sparklines to Excel 2003 and 2007. Microsoft has announced that sparklines will be a standard feature of Excel 2010.
Hat tip to Phil Greenspun.

You already can do some decent sparklines with older Excel versions and MicroCharts:
http://wwww.MicroCharts.net
Andreas