Modular Synthesizer for iOS
This looks like a great synthesizer for the iPad. Looking forward to checking it out. From their main page http://www.pulsecodeinc.com/modular.html it appears it will be available in the App Store on 9/12/13.
The main app will be free with IAPs (In-App-Purchases) to obtain modules as you desire, although they are promising a bundle IAP as well to purchase all modules at once.
Here's a demo teaser of the app in action: