It may be a bit large for your purposes, but the Berning Micro-ZOTL is wonderful head-amp. I used mine for much the same purpose as you describe - I brought mine on an extended road trip and it made for a great companion for my iPod and a pair of Sony MDR-3000 cans. Line-out of iPod via iDock into inputs of Berning. WAV files - not a bad way to pass the time in a hotel room when you're alone. As I mentioned, only downside is size.
Marco
Marco