Building a Comprehensive SF&F Collection

I'm giving a talk next month to an association of Texas librarians on how to build a good, comprehensive SF&F collection. I've given this talk before, restricting myself just to the science fiction genre, and am pretty confident with my list of works (both classic and contemporary) and what I have to say about it. Updating that speech with a few gems from the last year won't be hard. But this year, I'm giving two talks, one on science fiction and one just on fantasy.

So...

I'd really appreciate so