I'm horsey, but up in Manchester, so not that helpful. One of the best resources was my local BHS committee. I actually just emailed the chair for my area and asked about places to ride and she sent me a list! It did take me a while to settle somewhere (and, ahem, I bought a horse

), but it was a good start.
You might also have a look around the Horse and Hound forums as they can have some good info.