I'm glad you asked about putting apps into categories. I was thinking about doing a post on just that topic. An executive decisions has been made to make that the topic of my next post.
I know that Smarty Ears has an app called /r/ intensive SLP. The description of it states that it is for SLP use. At this point, I would hesitate to buy an app targeting sound production, unless one is looking for standard picture cards. Other than cards, the technology is not yet there to support apps for speech production that utilize the qualities of the iPad.