Plenty around Nailsworth.
Have a look at an OS map (bing will do). Just south of Nailsworth is Upper Barton End. Give all the trails around there a go.
The footpath from Shiptons Grave Lane to Orange Grove Barn is actually a permissive bridalway and has a nice descent.
The bridalway off Shiptons Grave Lane to Avening is another nice one. The wood to the north is worth a look.
For some nice long singletrack have a look in Stanley Wood (West of Nailsworth, just beyond Woodchester park). It runs parallel to the road. Selsley common is worth taking in, as is Minch.
Edit, this is what Tang was riding:
plenty of cheeky bits just not that long in duration. been riding up to uley via horsley and kingscote and joining the singletrack that runs next to the cotswold way to selsley, not bad and a good loop for the legs. still havent made it to wooton yet.
The cyclepath (old railway) is incredibly fast for linking things back together.
As for Wotton-under-Edge… check out Westridge Wood. It has at least as much to offer as Cranham.