Samsung Galaxy S with Voodoo or Speedmod kernel and Voodoo sound app.
Gives full control over the Wolfson WM8995 audio-hub. Improved SNR, lower IMD, choice between NOS or 128x oversampling DAC, reclocking, direct access to chip's analog volume control and so on.
And besides, the Galaxy S has native(!) MP3, AAC, AAC+, eAAC+, FLAC, WMA, WAV, AMR, OGG, MIDI, ... support. Storage is microSD, so plenty of space for the FLACs
Here's a few links:
http://forum.xda-developers.com/showthread.php?t=806195
http://www.head-fi.org/forum/thread/535134/for-the-galaxy-s-cellphone-owner
http://www.head-fi.org/forum/thread/533282/advanced-users-samsung-galaxy-s-kernel-sound-tweak