Airfoil for the Mac has been around for a long time, and has always been a great way to transmit audio in a fashion with more flexibility than Apple's own AirTunes (now AirPlay) standard. With Airfoil 4.5, the feature set has grown considerably, and Airfoil has fully joined the AirPlay client & server continuum.
Airfoil 4.5 will now allow your Mac to accept audio directly from any iOS device, meaning you can stream audio from apps on your iPod touch, iPhone, or iPad directly to your Airfoil-running Mac. Airfoil will now also send audio from iTunes directly to any AirPlay-compatible speakers. Finally, Airfoil 4.5 comes with several small improvements and additions to its remote control support.
Airfoil 4.5 is a free update for owners of Airfoil 4, and it comes with preliminary support for OS X Lion. It costs US$25 and requires Mac OS X 10.6.