I'm a programmer/engineer and have been working professionally in the technology space for 14 years. So I'm probably one of the more technical folks browsing this forum. I've read through this entire thread and there are a lot of solutions mentioned. One will work for one person and another won't.
I think there are several things at play with this issue and there are likely several different solutions depending individual machines and how they are used. The ideas and solutions around checking recent installs (like the alarm/lock dashboard widgets) are great ideas and seem to have worked for folks.
I started having this same problem today and I'm on a two month old Macbook Pro and have never, not once launched iTunes. This is my work laptop and I use streaming apps for music. So I was baffled at why iTunes would start launching on its own.
The first thing I did - before reading the forums - was checking my user account (Login Items) in System Preferences to see if iTunes was listed. Sure enough it was. I removed that quickly. I then went to my Music folder and deleted the iTunes directories (and sometimes iPod directory) which showed up after iTunes launched the first time. Then I kept working.
About 5 minutes later iTunes launched again. I use a keyboard app called LaunchBar so I started wondering if I had inadverently pressed a keyboard shortcut to play a song (even though I have no iTunes library) or something to that effect. I just kept closing iTunes after launched 2-3 times over a 45 minute period. And all the while I'd remove the Login Item if it showed up in System Preferences / Users & Groups.
Then I Googled the issue and as usual with Apple problems I wound up browsing these forums.
When I got to the comment where someone mentioned removing headphones from the computer causing the problem I kind of laughed a little. I thought that was certainly possible but probably very much an edge case. Then I looked down at my desk. Today I had done something I'd never done. I had my Sol Republic Jax headphones plugged into my Macbook Pro and routed beneath my keyboard. The keyboard was placed on sticky note pads to give the headphone cable a little room to move around. To get everything working comfortably I had moved the keyboard around some and shuffled the headphone cable around some too. All while the headphones weren't fitted in my ears.
I also saw in this thread where someone mentioned the headphone buttons integrated into the cord of some models including Apple and Sol Republic. I started wondering if I had inadvertently mashed the "next track" button on my Sol Repulic Jax headphones. I had since unplugged them from my laptop so to test I plugged them back in and then pressed the "next track" button. Sure enough, iTunes launched.
After checking System Preferences again and removing all the iTunes/iPod stuff from my Music folder I clicked the "next track" button a second time. And a second time iTunes launched.
Since today is the only day I've had this automatic (or zombie as one called it) iTunes launching problem, and the only thing different I've done is how I have physically used my desk, I think the headphone button was my issue. If for some reason this isn't the case I will certainly report back.
