We garden on clay - dry in some parts and waterlogged elsewhere. On the dry clay we have planted rhododendrons, poppies, rosa rugosa, berberis, buddlea, cotoneaster. We obviously improved the soil in the planting hole but have had some losses - a camelia looks very sick at the moment and I might dig it up and put it back in its pot. Where I can I prefer to dig the clay to try and break down the clods and add leaf mulch and compost - but its going to take 2/3 years to get really better conditions.
Perhaps garden above the clay by using raised beds or rockeries?