unlike other languages, a framework isn't as much of a requirement in Go since the Go standard library includes an http server, json serialization/deserialization, html templating, email, logging, basically everything you need in a web app. The url routing is pretty crappy, but that's my only real gripe. ngmoco's Falcore is worth looking at: https://github.com/ngmoco/falcore
Gorilla's mux adds much more capable and advanced routing. It's really nice to use it with subroutes, etc. Again, dead simple partly because it's designed well and partly because Go makes it easy to build.
