Hi
I used to have a garden with a similar problem. Although I can't say they ever looked particularly great there I had a variegated laurel and a lavender that seemed to just keep on going despite the awful conditions. Having said that, I was fairly new to gardening then and did'nt really do anything to try and help the soil. If I had've done they might have looked abit better. Sedum can survive in poor dry soil as well.

Nothing will grow terribly well if its less than 3 feet from the base of the trees, but you could try Lamiums and Ruscus.