For Mongo: Most people use mgo http://labix.org/mgo
For precog: dont know, but there might be something, but probably not.
I just forgot to say: a FRP* [0] Go equivalent of Play and that there's nothing like these upcoming Coursera courses [1] [2] for Go with examples.
[0] http://www.reactivemanifesto.org
[1] https://www.coursera.org/course/progfun
[2] https://www.coursera.org/course/reactive
For Mongo: Most people use mgo http://labix.org/mgo
For precog: dont know, but there might be something, but probably not.