Suggest few good seminar topics ...

1. Google App engine
2. Something on image recognition
3. artificial intelligence (or smart robots to make it sound catchy)
4. Rich internet applications
5. Parallel processing, and need for better parallel algorithms with the increasing number of cores for home pc, and also for better usage of supercomputers.
6. You can compare technology 10 years back and now, and what it's going to be after 10 years from now, it can be made a but humorous and you can maybe make the audience imagine of a day of there changed lifes after 10 years due to technology ( it would strictly depend on your skills to keep the audience interested)

Mine was "Bittorrent"