You can make a red dragon, orc, or elf and publish it in a book or module. They are all in the SRD.
Basically- if it isnt in the SRD, you can't use it under the d20/OGL. Anything else, you basically have to invent yourself. Like psionics for example. Before they were included in there, you could not use anything from the PsiHB. You would've had to invent your own system of psionics, psionic power, and psionic feats.
Not trying to shift the focus of the thread, but even I myself am a little unclear on exactly how it all works. A better place to ask is in the d20 Publishers Forum. Some of those guys are great at stuff like this (particularly Clark Peterson...he's a lawyer).
But- if you ever do wanna publish something and it includes something say from a previous edition of D&D (and it is not in the SRD), the best thing to do is to consult a lawyer.