DeveLinux is a Live Debian-based distribution oriented to developers and programmers.
DevelopGo is a complete development environment with extensive documentation and programming tools. It is a special flavour of OnebaseGo, meant solely for programmers.
Gendist is a live CD generator system. It has nice features like multi-distribution CDs, support for grub, isolinux, and gfxboot boot managers, and a modules system for configuring your distribution in live mode. This system is independent from the kernel version (but need unionfs and squashfs support). It only works on Debian Sid or Ubuntu Dapper.
The Lisp Resource Kit is a dedicated development/learning environment on a self-booting CD. It is designed to be an easy to use single resource for those who are interested in exploring Common Lisp, regardless of their experience or domain of expertise.
MiniKnoppix has only one graphical environment (KDE), its browser (konqueror), mail, web and news text based clients (mutt, slrn, links) and lots of tools for system administration (backup/restore, filesystem check/creation, security, network testing, and more).
The Mono Live LiveCD is a way for you to try out Linux, the Mono Framework 18.104.22.168, and the newest desktop applications without modifying your current computing environment.
NIOde is the Linux development environment for the Dutch Olympiad of Informatics. Although the system is especially meant for Dutch people, it's quite usable for non-Dutch people too.
Pollix is based on Knoppix. It includes many programming tools including J2SE SDK (full with doc), Jikes, Netbeans, Eclipse, BlueJ, JGrasp, JSwat, Tomcat, JBoss, Boa-Constructor, IDLE, SPE, VisualTcl, SWIG, SciTE, etc., and several Java, Python and Perl libraries.
SNAP Platform integrates the best open source Java components, into an easy to install toolkit, revolving around an open source JVM implementation, the Eclipse IDE, and Apache Tomcat. SNAPPIX is a Live CD Linux distro with a pre-integrated SNAP Platform.
Virt-P2V is a live CD or pxeboot image for migrating physical machines to virtual machine guests. It can be used to turn a Linux box into a Xen, QEMU, or KVM virtual machine.