I have been a fan of The Streets (aka Mike Skinner) ever since his debut 'Original Pirate Material' transfixed me with his moody and expressive rapping over trip hop/garage/dance beats.
One of the best tracks (and funniest) was "The Irony of it All" (you tube clip below). It explores the reasoning to legalize weed, buy comparing the peaceful nature of the smoker of the illegal substance to that of the legal beer swigging, fight starting, lager lout. Funny, but also make a wonderful argument.
For another great track about drug use check out ‘Blinded by the Light’, which also features a brilliant video.