For $60, you can consider the already recommended FiiO E11, or the JDS Labs cMoyBB (with 2x9V batteries if you prefer some extra power). The E7 has a worse amplifier than the E11 (it is similar to the $30 E6, but slightly improved, and includes a DAC), although it might be enough nevertheless if you do not listen to very dynamic music and/or at high volume.
The E11 is a good choice overall, its main disadvantage is that it does not work while the battery is being recharged, and it cannot be used with an external power supply either.
Edited by stv014 - 8/18/12 at 6:23am