The best answer I could find is http://www.debian.org/CD/faq/#search-for-package
The following question is also relevant http://www.debian.org/CD/faq/#list-image-contents
Maybe you could just download the jigdo files and look at them. They are very small.
$ ls -lah debian-6.0.1a-amd64-CD-1.jigdo
-rw-r--r-- 1 faheem faheem 31K Mar 22 21:39 debian-6.0.1a-amd64-CD-1.jigdo
From How Jigdo Works, Section 3.3,
Given an input of an ISO image and a
set of loose files which may or may
not be in the ISO image, jigdo-file
outputs a .jigdo file for that ISO
image. The Debian .jigdo files are
gzipped, so you need to use zcat or
zless to view them. Here's what a
.jigdo file looks like when you gunzip
it:
md5-0=http://somemirror.org/file-0
md5-1=http://somemirror.org/file-1
md5-2=http://somemirror.org/file-2
md5-3=http://somemirror.org/file-3