Flashbulb Interactions's Working through Screens is an excellent, well-illustrated ebook on concept design for designers and product developers. The key point here is how to use design tools and methodologies to get the right design for the problem.
Working through Screens is an online book for product teams creating new or iteratively improved applications for thinking work. Written for use during early, formative conversations, it provides teams with a broad range of considerations for setting the overall direction and priorities for their onscreen tools. With hundreds of envisioning questions and fictional examples from clinical research, financial trading, and architecture, this volume can help definers and designers to explore innovative new directions for their products.
Product teams can make significant progress toward these aims by changing how they get started on designing their products — by beginning with an emphasis on getting to the right design strategy and design concepts long before getting to the right design details.
There can never be enough discussion in the literature on this topic in my opinion, because understanding the problem and getting the right design is so important for success, especially when it comes to application design. The book is free to download, so check it out.