When you develop for AOS 4 you get a command-line-based development environment based on GCC 3.4 and the appropriate binutils. If you're not familiar with GCC then I'd only use it for C++; for plain C i'd use VBCC instead. Fortunately GCC is easier to install and configure on AOS 4 then on AOS 3.
As for programs currently being written see
http://amigaopenoffice.org/ to get involved with porting OpenOffice.org to Amiga.
OpenGL is coming soon and Warp3d is currently downloadable by registered AOS 4 users. Basic is currently not available as an OS4 native language unless you'd like to port SDLBasic.
If you want to program games on the Amiga I'd recommend you get familiar with the
SDL APIs and forget about DirectX in a real hurry. DirectX isn't portable to anything other than Windows.
Another option for programming is
Hollywood whose multimedia oriented scripting language compiles natively to machine language on AOS 3 (680x0), AOS 4 (PPC), MorphOS (PPC) and WarpUP (PPC on AOS 3).
