These are awesome tips! I like silence the best for focus (less cognitive load the better). These have been a godsend: http://www.amazon.com/3M-Peltor-H10A-Optime-Earmuff/dp/B0000...
Basically just your basic noise blocking headphones. For extra blockage insert earbuds under them. Sublime silence.
I'm not sure why it never occurred to me to get an inexpensive pair of earmuffs designed specifically for blocking out sound ($20), as opposed to a really expensive pair of reference-class headphones ($200+). Most of the time I just want to block out sound. And when I want music, I can probably put in my comfy earbuds and put the earmuffs over them. Thanks for the idea!