A Waterbury man has been arrested on drug related charges in Danbury.  Police launched an investigation months ago into resident complaints about illegal drug sales by 43-year old Gerald Blake Rockhead, who was known to the Special Investigations Division through past investigations and arrests.  He was stopped yesterday during what police say appeared to be a transaction, and found with 8 grams of crack cocaine in his underwear.  A Triangle Street apartment and a hotel room he was seen leaving, and had a room key to, were then searched.  Detectives seized 27 more grams of crack cocaine and drug packaging equipment.  Rockhead was charged with 2 counts each of possession of narcotics with intent to sell and possession of a controlled substance and possession of drug paraphernalia.  He was held on $150,000 bond.