Hi there.
Yep its pretty flat around here but some good XC rides and small bits of DH if you know where to look, Langdon Hills (Laindon) is very near.. Ive attached a pic of my last run there, the start point(s) on High Road (both off small dirt car parks have two nice small DH starts.
Danbury is quite impressive, a lot tucked into a very small space, check out this vid, its great quality and shows what fun it can be
,
http://www.youtube.com/watch?v=tc3-1t009OA.
The Olympic XC track is of course near too, Hadleigh (go to Benfleet or Leigh by train), there are lots of routes there, some short DH bits, I ride there a lot, but some of it is cut off now coz of the Olympics.
Andy