The Orban/Coding Technologies AAC/aacPlus™ Plugin is a free, full-featured software plug-in for Microsoft Windows Media Player. It is capable of playing AAC/aacPlus™/HE-AAC/eAAC+ audio files and streams in several standards-based, non-proprietary formats using the genuine Coding Technologies decoder. This is the good stuff from the company who invented the SBR technology to make AAC into aacPlus™. High quality, bandwidth-efficient audio is now a reality for Windows Media Player.

http://www.orban.com/plugin

Heres a list of AAC/aac plus streams to test and stuff :)

http://tuner2.com/wmp.html