In addition to MP3s, Winamp can handle pretty much any audio file format, plus line-in, and there is metric assload of amazing visualization plugins available for it (AVS, Milkdrop, Tripex, G-Force, etc.), so it's difficult for me to envision an audio visualization task that it can't handle. However, if you insist on a standalone vis, an older version of G-Force is available as a standalone application. (http://www.55ware.com)