Please read this to the end before drinking 
There are Beers labeled gluten-free, but what not so many people know: many non labeled Beers have little Gluten too. Others contain excessive amounts of it. Trial and error is not advisable for everybody. There are a few blog posts around the internet providing Data from different Sources on the subject. I tried to collect the data from a few sources into one comprehensive table. Please be aware, that much of it comes from home-test-kits used applied by people unknown to me and understand, that I can not guarantee for the soundness of the results at all. Also keep in mind, that production details of beer brands may change, resulting in changing amounts of gluten in the beer! So use it at your own risk!
I tried to keep the data as transparent as possible, thus introducing a new column for each new testing method/data source. I added a unifying 1 to 5 rating in order to allow sorting where 1 is a should-be-safe, and everything from 3 onward is not advisable for the gluten-sensitive crowd. This does not mean that a beer rated 1 is safe to drink for everybody! Where in doubt, you should visit the source of the data and make yourself a clearer picture on the reliability of the data!
Tip: Use the search function of the table to check, if your (former) favourite beer, or the choices on the menu you hold in your hands right now, have been tested.