Someone recently wrote me, asking for the old CodeView format. I told him that it was readily available on the web. He subsequently wrote back and said he couldn't find them.
So, using both MSN Search and Google, I dug around and was able to find the spec, but in only one place. And I only found it because I knew lots of key words in the spec that the average person wouldn't.
So, for posterity's sake, here are two useful links:
For the Microsoft (CodeView) spec: http://www.x86.org/ftp/manuals/tools/sym.pdf
Another useful spec: The Intel OMF format: http://www.x86.org/ftp/manuals/tools/omf.pdf
Note that these documents are old, and very likely don't have the latest and greatest additions.
Also note that these days, we're pushing people towards the DIA SDK: