The battery-powered Pocket Rock-It S1b is a bass headphone amp that allows you to practice silently anywhere.
It has a rotating input plug with 90 degrees of motion, so it can plug into any bass guitar jack with no cable needed. It has a line-in to connect a CD/MP3 player, iPhone, etc. for play along practicing.
This item is "as new" and includes brand new headphones. I received it as a gift but I don't really need it.
$33 OBO via Paypal including shipping.