Here are a few useful links to official websites in the categories of General, Other Mapping, Museums, and Sites
General
Official website for Hadrian’s Wall Country
Hadrian’s Wall Path National Trail Information about the National Trail
National Trust Hadrian’s Wall and Housesteads The Trust own Housesteads and English Heritage manage it for them
Northumberland National Park Hadrian’s Wall The Wall is in the National Park and they are one of the partners in the shop/visitor centre at Housesteads car park
Car Parking in Northumberland National Park Parking is ironically a mess along the Wall with no overall scheme that covers Cumbria, Northumberland, and Tyne & Wear, but this deals with the National Park bit
Other mapping
Some useful lidar mapping of Hadrian’s Wall (but leaving out the east end for fairly understandable reasons) by Dr Steve Malone, with an explanation here
More mapping of Hadrian’s Wall using lidar and a number of other means (which does include the east end) by Robert Langdon
Museums
The Great North Museum Wall finds from Northumberland and Tyne & Wear
Chesters Museum finds from the Clayton estate (Chesters, Carrawburgh, Housesteads, Vindolanda, Great Chesters, Carvoran)
Vindolanda Museum finds from Vindolanda (Chesterholm)
Housesteads Museum finds from Housesteads
Tullie House Museum Wall finds from Cumbria
Senhouse Roman Museum finds from Maryport
Segedunum finds from Wallsend
Sites
Hare Hill English Heritage free entry
Banks East turret English Heritage free entry
Pike Hill signal tower English Heritage free entry
Leahill and Piper Sike turrets English Heritage free entry
Birdoswald fort English Heritage entry fee
Poltross Burn milecastle English Heritage free entry
Carvoran Roman Army Museum Vindolanda Trust entry fee
Walltown Crags English Heritage free entry
Vindolanda fort Vindolanda Trust entry fee
Housesteads fort English Heritage/National Trust entry fee
Sewingshields Crags English Heritage free entry
Carrawburgh mithraeum English Heritage free entry
Black Carts turret English Heritage free entry
Chesters fort English Heritage entry fee
Brunton turret English Heritage free entry
Heddon on the Wall English Heritage free entry
Denton Hall turret English Heritage free entry
Benwell Vallum crossing English Heritage free entry
Benwell temple of Antenociticus English Heritage free entry
Wallsend fort Tyne & Wear Museums and Art Galleries entry fee