It's kind of amazing where songs come from sometimes.

On some occasions it's just been me sitting at a computer and forcing something to happen.
On other occasions, I'll be out riding my bike and a song will just come to me that gives me that 'homesick' feeling.
Other times, I'll be at a party, listening to some DJ music and coming up with a whole bunch of riffs and changes that I could have added to the song.

I'm not trying to push this song or anything cause it's probably about 10 years old by now but this is a good example of a song that came out of nowhere:
I was imagining what it might be like to be a father, singing a lullaby to my daughter (neither of which I was at the time), and the whole thing wrote itself in about 10 minutes.

http://s93744050.onlinehome.us/MP3s320/GoodnightMyLoveFemale_Schmange.mp3

Totally opposite to my usual style of hard rock. All the harmonies were done by myself using 16 tracks, and the girl who sang on it was 3000 miles away recording it in a closet at home.

Weird thing is, out of all the songs I've got posted on iTunes, this and the instrumental of it are my top sellers.