Some more suggestions, now that the existing answers are quite old:
- https://github.com/op/go-logging – smaller than the other here
- https://github.com/sirupsen/logrus – used in many popular projects such as Docker
- https://github.com/inconshreveable/log15
- https://github.com/golang/glog – from Google, implementation of their C++ glog library in Go
- https://github.com/go-kit/kit/tree/master/log focused on “structured logging” which is better for tools to consume
- https://github.com/uber-go/zap – “blazing fast”
- https://github.com/rs/zerolog – zero-allocation JSON logger