If you want to code in C++, I wouldn't recommend StormC3 (that is included on the DevCD), as it's support for C++ is very limited.
The best development environment for the Amiga right now, is IMO StormC 4, which uses a modified GCC compiler with very good support for both C and C++.
But, if you don't want to spend a lot of money getting started, I would go for GCC 2.95.3 as someone else suggested.
The DevCD is definately worth buying too, so you get the correct system include files and some documentation...
