There are many white horses in Wiltshire (
http://wiltshirewhitehorses.org.uk/ ) - the ones at Pewsey and Alton Barnes I used to see regularly when I loved out there. Also one (very famous) at Uffington in Oxfordshire - which I think is the oldest in Britain.
The regimental crests on the way to Compton Abbas are at Fovant, and date to the WW1 Pals regiments.
There's a chalk cross at Dunsmore, which is a hill to the SW of Aylesbury I think (somewhere near Wendover). There was a bomber crash there during WW2, although I'm not sure if the two are connected.
G