Well my inspiration comes from many sources I suppose. I too sing/whistle/hum in the shower too! don't we all though? (even the one's who won't admit it, do too! XD) My girlfriend inspires me too. I get inspiration from some really simple things too when I'm out and about I sometimes think up melodies, which kind of come from the surrounding noise around me.
Sometimes I take inspiration from the negative things that can happen too, (though I rarely write music that reflects such negativity) instead I find I can do quite the opposite with the negativity. Time to Reflect (My Piano Piece) was written when the chips were down.
A lot of the time though too I derive inspiration from other music I hear. I have an eclectic taste and often find stuff that leaves me wondering just how the hell it was achieved. whether it be music I've heard here on the AP or from signed artists. It all adds to the things that I find inspirational!
anyhoo as you were!