Projects that can be performed by FPGA based signal processing, have no border and no end. With the advancement of technology, field of FPGA applications is rapidly expanding. There are many new fields to work with FPGA such as :
MIMO detection in digital receivers, ICA, matched filter, sonar applications, Blind channel equalization, image and audio processing, DVB, Advanced channel coding techniques, Pattern recognition, and ... .
In addition to the topics proposed by Mohammed Mobien, I suggest you to check out related articles about FPGA implementation of Image Encryption methods.