Where have you been? :-) Sun has dropped their old K&R C compiler, supposedly to create a market for multiple compiler suppliers to provide better performance and features. Here are some of the contenders:
1) Sun Studio C:
This is the compiler which is used for Solaris development; includes various compilers with x86/amd64 support (and SSE/SSE2, etc)
Various licensing schemed.
Apogee sells C, C++, f77 and f90 compilers, mainly for SPARC. These compiler include the KAP preprocessors from Kuck and Associates.
3) Gcc.
Gcc is available from the GNU archives in source form. You need gcc 2.3.3 or later, and you should prefer gcc 2.8.0 or later as it works better with Solaris 2.x include files. You should not use GNU as or GNU ld. Make sure you run just-fixinc if you use a binary distribution. Better is to get a binary version and use that to bootstrap gcc from source.
Solaris 10 includes gcc in /usr/sfw/bin/gcc; this compiler was used to build the AMD64 bits of Solaris 10.
GNU software is available from (unchecked URLs):
prep.ai.mit.edu:/pub/gnu
gatekeeper.dec.com:/pub/GNU
ftp.uu.net:/systems/gnu
wuarchive.wustl.edu:/mirrors/gnu
nic.funet.fi:/pub/gnu
When you install gcc, don't make the mistake of installing or GNU libc, they are not as capable as their counterparts you get with Solaris 2.x.
4) Info on other compiler vendors will be added if you send us some.