Given a reasonably powerful system, the hardware doesn't care what lanugage you're writing in. You could program Saturn with
Brainfuck or
INTERCAL, *if* someone were to write the appropriate compilers/interpreters (and if you were sufficiently intelligent and/or masochistic). In terms of tools that exist right now, I'm only aware of assemblers, and compilers for C and C++. There's also a BASIC interpreter or compiler, but I've never actually seen it. It might be possible to use GCC to compile Fortran, Objective C, and maybe Java, but that would probably take a substantial amount of work to get running.
edit: as for the others, C is the best bet for Dreamcast, and assembly language for everything else. There's a C compiler for Genesis, but I've never tried it.
(Edited by ExCyber at 10:15 pm on Jan. 19, 2002)
(Edited by ExCyber at 10:16 pm on Jan. 19, 2002)