MadOnion.com Oy is a Finnish company that specializes in computer benchmarking. It originated in Remedy Entertainment, that made a program called FutureMark - that was split into a company of its own, as Remedy is more of a game company. FutureMark then became known as MadOnion.com.
Their most visible product is 3DMark that has quickly become the standard in gaming circles for testing 3D graphics performance of PC hardware. 3DMark programs are freeware; the "pro" versions that also include other more specialized tests like image quality are sold commercially. The use and availability is so wide-spread that some games include, in addition to recommended hardware configuration, the recommended 3DMark rating.
What's so special about their benchmarks is that they cooperate with both hardware manufacturers and game developers - and use realistic game engines as the basis. For example, 3DMark 2001 uses Max-FX, the graphics engine used in Max Payne. Also, their benchmarks are far from boring; People who make these benchmarks have a demoscene background. (One of the complaints about 3DMark has been that real games don't look that cool compared to it =)
Aside of game benchmarks, they also have video (Video2000), application (SYSmark2000) and web server performance (WebMark2001) benchmark products.
Update, December 2002: MadOnion.com has changed their name to Futuremark again...