The best way I know to chase sadness away is to work on something while singing really loud to music.
In one of the more recent reincarnations of iTunes, Apple added what is now my favorite feature: the Genius button. While it can be used to find out what other music you can buy, I mostly use it to generate playlists that revolve around a certain theme.
Ever since I got my first (5gb) iPod, I've used the Shuffle feature to play random selections from my library of music. But as even Apple noticed, it's too random. So, I created subsections of my library and then used Shuffle on that. That works pretty well. Apple tried to make it better by letting you control the randomness, essentially making the shuffling less random and more like the first song you chose. That feature was confusing and didn't really seem to make a significant difference.
The Genius button does what the "less randomness" feature was aimed at: creating a playlist of songs that go together well. You choose a single song and then Genius looks through your library and chooses other songs of roughly the same genre and type. How does it know? According to a blog posting in Computerworld, Apple analyzes the songs in your library, and compares them with the data in its own database of music to figure out compatible tunes.
For example, suppose I choose "Things We Said Today" by The Beatles:
Then I click the Genius icon in the lower right corner of iTunes:
And voilà, iTunes generates a playlist for someone in the mood to listen to "Things We Said Today":
If you don't like the songs that were chosen, click the Refresh button to generate a new list.
If you love the list it creates, you can save it as a regular playlist. (This way, it won't be erased the next time you use Genius.) Simply click the Save Playlist button. The playlist will have the Genius icon and the name of the song from which it was generated.
You can also copy Genius playlists to your iPod and iPhone, or indeed, create them there in the first place.
Then all that's left is to play it loud, and sing.