However if you wanna play with languages you're less familiar with, I'd recommend Go, or Node.js.
Personally I find Go really interesting as it's quite different from the languages I normally work in, and it's concurrency model makes it performant without being a mindfuck.
Node.js is interesting as it's Javascript, but extremely I/O performant due to it's evented nature, but that also makes concurrency a bit of a mindfuck at times.
Those are my suggestions at least if you're itching to get your toes wet in some new fun languages :)
So I'd say, if just want to get a simple CRUD API app out quickly, use Python and Flask or something similar as it's something you already know well. If you wanna use the CRUD API app as an excuse to play with new languages and technologies which will hopefully lead to a expanded skill-set, then go for Go ;)
As for Node.js, if you already know Javascript, it'll fall about 30-40% of the way between using Python that you know and Go that you don't know.
With that said, I wouldn't brush off Python as a possible choice. Here are some small/lightweight Python web frameworks in addition to Flask (http://flask.pocoo.org):
1. Bottle (http://bottlepy.org). It's a one file module and has no dependencies.
2. Web.py (http://webpy.org). The "anti-framework." Very simple.
3. CherryPy (http://www.cherrypy.org). Another minimal framework that comes with its own WSGI server.
All the frameworks mentioned above are stable, mature, and used in production. With that said, any good API these days needs authentication, authorization, and rate-limiting. To get these standard things done from the start you should look at fantastic Django Rest Framework (at least don't ignore it). If you do use Django, then you can also use Haystack (http://haystacksearch.org) to easily work with Elasticsearch.
It's hard to give detailed suggestions without knowing the application you are trying to build, but I hope you find this helpful.
I've also noticed that Haystack's owner has been inactive recently which concerns me. This in itself gave me a reason to check out Elasticsearch's own Python bindings[2] which aren't that scary after all.
I am looking at Gorilla web toolkit (thanks for the link!).
When you have it nailed, try to do it in something else!
I have no experience with it, but what about elixir-lang.org? Everyone try GO or Node. Be more brave and be more niche!
Also, I'm learning a bit of F#. Is so crazy, and is .NET. So, how about be against the trends :)
If nothing else you'll be introduced to a lot of programming concepts you'd otherwise be unlikely to see.
It is written on top of Flask and includes some batteries.
Could get a simple API up in 2 hours.
Learn a little Lua along the way. Really great stuff!
