I went to a Computer Science and Engineering Day at the University of Nebraska today and now I feel really motivated to program something. The only problem is, I don't have any idea of something to write. Is there some special trick to coming up with ideas for new programs?

here are some good places to help out

or how about subscribing to the java newsletter published by sun
click on newsletter link in the box on the right and see what little snippets of code they share with you and see if you can expand on it.

or heck if you are a real good java developer why not try and help out developing Mustang (J2SE 6.0). And to think 5.0 was only released in october-november. Honestly I can't think of anything better on a resume than saying I was a contributer to J2SE 6.0!!!

I'm not into writing things in a day, most projects take a long time and are for a definite need.
But then I do most writing for a living so the company decides what needs be done :)

Why dont you try making an mp3 plyer, its easy to actually play the mp3s using java classes, then you could use file io to scan a folder for mp3s, you could have playlists and loads of other stuff. It should be fairly simple to start and you can even do one from a cmd line so if you dont know GUI's yet you could still do it and then when you learn GUI's you could just update it.