British and Commonwealth Badge Forum. A very useful forum that hosts a range of discussions and information relating to a broad range of military badges and insignia.

http://www.britishbadgeforum.com/

Great War Forum. This discussion based forum has plenty of photographs of insignia as well as soldiers in uniform.

http://1914-1918.invisionzone.com/forums/

Imperial War Museum. A huge resource of historical information relating to Britain and the Commonwealth. 

http://www.iwm.org.uk/

Military Historical Society. The Military Historical Society promotes the study of the history of the uniformed services of the Crown, of uniforms, weapons, and all aspects of military history.

https://www.themilitaryhistoricalsociety.co.uk/

Military Heraldry Society. The Military Heraldry Society is aimed at collectors and historians that have an interest in cloth badges.

http://militaryheraldrysociety.com/

Sell My Militaria. A Free website where militaria and badge collectors can buy and sell items. 

http://www.sellmymilitaria.com

World War 2 Forum. A discussion based forum relating to all aspects of WW2.

http://ww2talk.com/

York and Lancaster Regiment Museum. This is THE place for information relating to the York and Lancaster Regiment. It is based at Clifton Museum in Rotherham and has displays of medals, uniforms and equipment used by the Regiment. 

The Regimental Collection – Clifton Park and Museum 

York and Lancaster Regimental Archives. The Regimental Archive is based in the same building as the museum. It is a superb resource and contains thousands of photographs, personal documents and materials used by the Regiment. If you are visiting South Yorkshire, a visit to the archive is essential.

The Regimental Archive – Clifton Park and Museum 

A website about cap badges worn by the officers and soldiers of the Essex Yeomanry and other military units across the County of Essex.

https://www.essexmilitarybadges.uk/