Blackmask Online
http://www.blackmask.com/cgi-bin/newlinks/page.cgi?d=1
Free. large variety of ebooks in many formats (MS-Reader - Acrobat - Rocket eBook - Zipped format - iSilo - Mobipocket). No native Palm format (other than the worthless iSilo and Mobipocket), but the Zipped (HTML) format can be easily converted.