I have seen in books, articles, blogs, and forum posts that the weeds I have can tell me a lot about my soil.
However, aside from some relatively obvious ones regarding soil compaction and tap roots, I have yet to find any good resources. Especially for soil characteristics I couldn't tell by looking at or feeling the soil. I have a few notes from my own gardens, but they are largely suspicions and hunches.
Anyone know where I can find more in depth information?
The soil and health library has an enormous free, legit, out-of-copyright online catalogue.
It's really cool!
Aside from just being a good place to poke around, do a search for 'Weeds'.
Weeds, Guardians of the Soil by Joseph Cocannouer is an American classic.
Weeds and What They Tell [Ehrenfried E. Pfeiffer] used to be there, but it must be back in print.
It's very old, but the plants haven't changed and he's a biodynamic guy, so no "dump a load of 2-4D on it"...
Actually, I very much suggest investigating biodynamic literature generally for weed info.
This PRI thread might be helpful.
Most resources I know of aren't American, but we tend to share weeds wherever there's 'the white man's footprint'