Below is a list of useful sites that can be found on the internet regarding Enduro & Motocross racing:

Bob Mullins EnduroNews (The main UK site for the UK Enduro scene)

The Auto Cycle Union (UK Motorcycle sport main authority)

The Amateur Motorcycle Association (another UK offroad race organisation)

Adrenalintrip.net (ultimate forum site for all things extreme sports, Massive motocross & enduro section)
also known as www.mxtrax.co.uk (for the off road biking bit)

British Armed Forces Motoring Association (BAFMA is the body that runs combined services events)

Bikers south west site (off road site for the south west region)

Dirt Bike rider magazine

www.MXCam.co.uk (motocross video action)

Trail Bike & Enduro Magazine (good forum here)

Track N Trail Race series

Trials & Motocross news