don't go for complete products like a complete system or so .. go for a close-ended project .. small but covering all design aspect .. and don't expect to sell it, cuz some student think they will sell their project and then they start optimize in one direction leaving the project open-ended ..
try to chose a project that covers the following :
1- system level modeling .. like modeling using matlab or C
2- RTL Design ( VHDL or Verilog )
3- RTL Verification ( VHDL or Verilog )
4- Synthesis ( using known tools like Design Compiler or Build-Gates or even Lenrado Spectrum )
4- back end physical design ( try to go thru the automated flow )
5- have a look at the Floor planning, Place and Route, Extraction .. etc.
6- try to understand some concepts like design for low-power .. design for test (DFT) .. Formal Verification .. Post Synthesis / Post layout Simulation .. etc.
7- try to deal with as much tools as u can .. if applicable ..
This is the best way to gain knowledge and attract companies after graduation .. they won't love u if u filed a patent in the graduation .. but they will love u if u know the complete design flow ..
Topic Suggestions :
1- FFT/IFFT
2- Viterbi Decoder
3- 8051 Microcontroller
4- DCT/IDCT
don't go for bigger projects cuz these things are already big ..
wish u the best of luck