From http://www.mpesch3.de/: 1by1 is a small and versatile audio player for MP3 and dll/plugin supported audio formats like WAV, OGG, MP2 or CD Audio. Without the need for a playlist it plays multiple files from a directory or a whole disk. You can simply handle and play your tracks in the file list view, load them through the command line (e.g. if associated with file type) or drag them over the window.
1by1 allows you to replace the buttons with your own by creating a bitmap. I made a button strip using the Silk Icons from famfamfam.
Here's the PSD if you'd like to change the background color to match your system. It looks pretty good with the white background but if the very slight jaggies bother you, you can fix it using the steps below.