There is LOTS of stuff in Roppongi that is not a tourist trap. For starters, avoid anyplace that a tout tries to get you to go to. Actually a few of them are legit, but there is no reason to take a chance and see if you get lucky. I'd say starting at the Heartland Brewery in Roppongi Hills -- if you can find it -- will do just fine. Other places where you won't encounter a door charge and will find reasonably priced drinks include Geronimo Shot Bar, Quest, anything with "Gaspanic" in the name (although that's mostly for people under 25), Paddy Foley's, and even Motown I or II.