I just downloaded an app called Articulation Station (by Little Bee Speech) that I think will be great for my ds with articulation difficulties. It's a simple app, but the speech is clear, the graphics are good, and the presentation is uncluttered and well-organized. It presents the speech sound in isolation, then progresses through activities at the word, sentence, and story level.
We are working on /p/ at the moment and that sound is offered as a free sample. The rest of the sounds can be purchased separately. I don't plan on buying many, but will probably purchase a few of the sounds my ds has the most trouble with.
I'm not affiliated with the product in any way, just wanted to share in case anyone else might find the app to be helpful.