For folks who are seeking wildlife rehab, here's a directory link that also has some useful tips.
For an eloquent write-up on the scientific value of dead birds, "So You Found a Dead Bird" says things a bit better than I generally do. I would say that in some cases, there is such a thing as too common (but probably not for under-studied counties), and there is such a thing as "too far gone" for roadkill/decay/etc - but that also depends on the bird. Snow Bunting roadkill in TX? Only a wing or leg still 3D? Bring it in!