Matthew Robbins released Harmonizr, a new AUv3 harmonizer effect with a lot of nice voicing options. In addition to AUv3, Harmonizr arrives with MIDI input so you can manually specify the harmony from a keyboard.
Harmonizr iTunes Description:Harmonizr is a vocal harmonizer offering a unique and fun user interface. You can sing a melody, setting the appropriate key centers, and Harmonizr will do the rest, giving 3 voices of automatic harmony. A preset mechanism allows you to change the harmonization, and an editor allows you to customize how you want to harmonize each type of key center (major, minor, and dominant). Harmonizr also supports MIDI input, both to detect key center, and to provide a mechanism for keyboard players to manually specify harmony. There is a 10-voice limit in manual harmonization, and it can be used in conjunction with the automatic voices to create a richer sound, with a total of 14 voices.