The only one I've seen that is explicitly fanless and has good capacity is the 1TB LaCie "design by Neil Poulton" (who?) but it's a bit bulky and it has quite a few bad reviews on Amazon.
Wow... I just happened into this thread and saw this. This is the EXACT external drive I have sitting on the desk with me. This thing is dead quiet unless you're explicitly trying to listen for it. (Right now I'm having a hard time hearing it over my PSU fan.) And, remarkably enough, it's very cool to the touch despite being fanless. (My initial concern was heat, but the whole case acts as a heat sink, so there's no hot-spots to speak of.)
As for bulky, sure it's a little big at 7" tall, but I have it sitting behind my monitor, so no desk real estate is taken up. Added bonus: the status LED/"one-touch-backup-button" isn't terribly bright, so there's no big blue spot behind my monitor.
I only wish I had a USB3, FireWire, or eSata ports on this computer... C'est la vie...
