This paper suggests tools that provide significant improvements in the design and verification of FPGA-based digital circuits. These tools include reusable specifications of hardware components (modules) that have been proposed for two types of CAD environments; Xilinx ISE 5.x and Celoxica DK1. The components can be employed to implement both application-specific blocks from the selected area (mainly from the scope of combinatorial computations) and a number of interfaces that are very useful for interaction and data exchange with devices attached to a FPGA, such as LCD and touch panels, bus controllers, etc. The designed modules can be easily integrated into any application-specific digital system and used for visualizing the results, fast data transfer, debugging of internal sub-circuits, etc. They were constructed in such a way that their functionality can be either fixed or modifiable (both statically and dynamically). The latter capability was provided with the aid of re-loadable RAM-based blocks. To illustrate the capabilities of the tools suggested, four design examples are discussed. Additional materials for this paper are available in the form of a number of tutorials and projects for FPGAs that can be accessed through the Internet.