AudioXplorer now has preliminary support for Audio Units (AudioXplorer is an AU host).
The following links should provide a good start to find Audio Units Effects:
The Effects menu in AudioXplorer will display all available Audio Units Effects (as well as custom plug-ins).
To display the parameters window of each Audio Units Effect or custom plug-ins, hold down the Option key while selecting the Effects menu.
Custom plug-ins SDK for AudioXplorer are available now. They allow any programmer to develop plug-ins for AudioXplorer in a few minutes without specific knowledge of how plug-ins are working.
Download the SDK here (requires the MacOS 10.2 Developer Tools).