C++
1. StormC 4 is a fully functional C++ compiler based on GCC. It also has an STL implementation. It is somewhat expensive.
2. The GNU Compiler is free on aminet but a mess to configure and is very slow. However, if you need C++ and don't have the cash for StormC 4, then this is really your only option.
C
1. SAS/C is considered by many to be the best C compiler for the Amiga. Ithas an editor called SE, but SE is not really easy to use. It is very UN*X like and is a dream to use even on the command line. The latest version is 6.58. It is not sold new anymore so you will need to find it second hand.
2. HiSoft C++ has what I consider the best IDE for the Amiga. Its C++ implementation is old so I'd only use it for ANSI C coding. Understanding the compiler message are a bit difficult sometimes, but it is possible to make some good software with this setup. No printed documentation, but decent electronic help.
3. vbcc is a little C compiler that is free and easy to use. You will need to get the Dev CD to use any amiga libraries though. No IDE.