One word: porn . . . . Nah, just kidding. I'd probably fill them with internet marketing ebooks from mr. Imram Naseem. Would take about a week...
I will store all my favorite movies, songs, software, pictures, some technical videos, e books, and all discovery videos and as well as documentaries.
I would put them on my bicycle, they would look awesome on it Nah, I'm pleased with my current hard drive space so I'm doubting that I can fill 2x2TB hard drives, but it wouldn't hurt to have those.