MP3 decoder
http://www.pjrc.com/tech/mp3/sta013.html Good MP3-player design documentation
http://www.st.com Search for STA013 to find datasheet

DAC
http://207.87.22.21/design/products/overview/index.cfm?ProductID=184 Information on CS4334

ATA/IDE/ATAPI hardware interfaces
http://www.t13.org The standardization organization responsible for ATA/ATAPI

ISO-9660/JOLIET file systems
http://www.alumni.caltech.edu/~pje/iso9660.html Good explanation of ISO-9660
http://bmrc.berkeley.edu/people/chaffee/jolspec.html Odd but useful JOLIET specification

Other
http://www.lge.com Manufacturer of CD-ROM we used, website has minimal specifications
http://ata-atapi.com/atade.htm ATADEMO, a very useful ATA/ATAPI demonstration program

My hard drive died in the middle of this project so I lost many very useful reference documents, probably the most useful was the Small Form Factor (SFF) committee's SFF-1080 document which was the best reference for ATAPI commands and interface.