Not only excellent library support, but also a large array of productivity tools ranging from superb IDE, static code analysis, build+dependency tools, great Continuous Integration, etc.
You should look at the work on pypy; specifically the RPython subset of python. It uses type hinting for static type analysis for the JIT compiler. It's not as hardcore as a fully statically typed language like ML or C but it will catch mistakes in mixing types.
Not to push the issue, but Go's standard libraries are fairly decent for being minimal and are dead simple to use. The docs have a good mix of examples and quickly parseable information.
I'm extremely happy with nsf's gocode [1] adding auto-complete support to Sublime Text and Vim. It's quite nice. Go, itself (from `hg`), has syntax support for vim and (I think) an emacs plugin. There's also a Goclipse modified Eclipse install which I don't know much of anything about.
There are others, [2]
I mean, there certainly isn't a complete equivalence of Eclipse for Go (yet?).