Scheme and Common Lisp are standardized. SBCL seems like the defacto open source lisp and there are plenty of examples out there on how to use it. It's fast and free. ClozureCL also looks pretty darn good.
PLT Scheme seems like the defacto open source scheme and there are plenty of examples out there how to use it. It's fast and free.
The CL HyperSpec seems as good as the JavaDoc to me.
As far as community fragmentation I think this has little to standards or resources. I think this has far more to do with what has been a relatively small community until recently.
Clojure I think has a good chance to become The Lisp for the new generation of coders.
Perhaps my point is a very popular implementation is all that is required to give the illusion of a cohesive community.