Major and Mrs. Holt’s Battlefield Guide to the Somme.
The Somme Battlefields – Martin and Mary Middlebrook
The First Day on the Somme – Martin Middlebrook.
Somme – Lyn Macdonald.
The Somme – Anthony Farrar-Hockley.
The IWM Book of the Somme – Malcolm Brown.
Forgotten Victory – Gary Sheffield

Publisher Pen & Sword has produced a series called Battleground Europe with many on the Somme. Most include car and walking tours. An excellent overview in the series is Paul Reed’s Walking the Somme.

Good maps are vital. Most detailed is the blue IGN 1:25000 series. Four cover the 1916 Somme: 2407 ouest, 2407 est, 2408 ouest & 2408 est.
Good for general use is the 1:100000 Laon/Arras map 4.
The Commonwealth War Graves Commission has a 1:200000 Michelin map overlaid with its cemeteries and memorials. Number 53 covers the Somme.

World Wide Web
For more information try the following:
The Old Front Line
Western Front Association
The British Army in the Great War 
The Somme Tourist Board
The Great War Cemeteries Project
Salient Points. Great site with info about the Ypres Salient.
An Unfortunate Region.
Achiet-le-Grand during the Great War..
Friends of Lochnagar Crater..
The Somme Association.
B&B in Flanders at Vlamertinge – Brandhoek near Ypres.
Medal Framing
Poppy Medal Framing can frame your medals (Pip, Squeak and Wifred) and the Death Plaque. Find them at this link:
Poppy Medal Framing