What is your domain and what are the languages you know , and What do u want to become (ie what is ur carrier plan) are more important. and your project should reflect that only.
Your question is really silly. because it is missing some very important elements.
1. What is your objective to do the project.
2. What is your expertise.
3. Time frame.
4. How much you know about the OS
5. Do you have access to some local guru.
6. etc ......
Now your next question.
You can made a decent project using either
1. apache & php
2. C++ & QT
4. Implement Servers. such as Mail Server, PDC, CVS ....
5. IPv6 Applications.
6. And thousand or more projects.
Provide some more information so that we might help you.