One of the OpenSource projects I work on, Apache Traffic Server, supports Solaris. I build on OmniOS for this development, and as much as I like it, it's semi-difficult to setup a development area properly. I'm likely missing something (like, a developer bundle or meta package), but these are the packages I find necessary to always install:
$ sudo pkg install gcc51 header object-file
Note that GCC installs in /opt/gcc-<version>, and without object-file autoconf / configure does not behave well. In addition, I use the OmniOS additional package repository as well, for goodies such as Emacs:
$ sudo pkg set-publisher -P -g http://pkg.omniti.com/omniti-ms/ ms.omniti.com
Software installed with this goes into /opt/omni.
Update: For some details on getting network setup on your OmniOS box, see http://blog.nemtallahdaher.com/wordpress/?p=127 . In addition to this, I also had to update the nsswitch.conf file of course (just copy over the DNS version of it).