Amazon supports AZW, TXT, Audible, MP3, MOBI and PRC on the Kindle, and the Kindle DX adds PDF to that list.
Sony's Reader Daily Edition (pictured) supports PDF, EPUB, Word, BBeB book (Sony's proprietary format), TXT, RTF, MP3 and AAC.
Plastic Logic's reader will support PDF, Word, Excel, PowerPoint, JPEG, PNG, TXT, HTML, BMP, RTF and EPUB.
It might be a lack of support for EPUB that hurts Amazon in the long run. EPUB, the open e-book standard format adopted by the International Digital Publishing Forum in 2008, has been adopted by every major e-reader maker except Amazon. Sony has already seized upon Amazon's hubris -- Sony's Steve Haber, president, Digital Reading Business Division, noted earlier this month: "A world of proprietary formats and DRMs creates silos and limits overall market growth. Consumers should not have to worry about which device works with which store."