the future of libraries in the digital age
Wow... Not an easy answer to this one. I did check out your site and it's full of great resources. As you mentioned yourself, it's really up to the librarian/media specialist to find out what the teachers are studying, and then to provide resources. For whatever reason, teachers tend to "forget" that the librarian is there as a resource person not just for students, but for teachers as well.
In one school where I taught, teachers were required to submit units of study to the school librarian so that she could assist them in finding resources. Sounds onerous for thee teachers, but it wasn't, since you only needed to submit topic names (maybe 4 to 6 for Science, 7 to 8 for Social Studies, and so on). The librarian then met with teams during their planning periods to clarify topics, and begin offering resources. A class studying polar biomes, for example, would love to know about Beyond Penguins and Polar Bears. Totally win-win.
I think a way to make your site more user-friendly is to try categorizing by topic and theme, along with science discipline and grade level. A teacher Google searching for ideas will more likely find a site whose "architecture" is designed in terms of the topics being sought via search engines, rather than in terms of strict scientific disciplines.