RealNetwork's Media Player (A Linux port is availible). Although critized and often told as being bloatware, it is one of the few media players around that was able to rival the Windows Media Player releases effectively as they came out.
RealPlayer 10 was the media player to replace RealOne player (which is also known as RealPlayer 9). It includes some extra features and GUI improvements. There are three varients: Free, Pro, and SuperPass Premium.