Soundsgoodtome
Headphoneus Supremus
On sale now for $44 shipped: http://head-direct.com/Products/?act=detail&id=216
Honestly, something like the Fiio E11 can drive them very well. You don't need a powerful amp to drive them. The Fiio E11 has low and high gain settings as well. I think you don't need something more than a 150ohm amp to push these to its full potential. I had them hooked up to my SB Z and I had to keep the volume around 25 to 30%