Nothing yet. The Defender is a tricky one to redesign, perhaps the trickiest of all, because it is still the most iconic representation of the brand's storied past, and its owners are generally the most hard-core, loyal, and... resistant to change. The DC100 concept they came up with in 2011 was not received very well, so they must have gone back to the drawing board on that one. I think they will concentrate on finishing up the Discovery line first, and tackle the Defender last, probably in 2-3 years as David says.
I completely agree with Umberto. The Defender will really make or break some of the hard-core followers.
I posted previously about my conversation with a LR employee who was recently at a meeting at the LR headquarters in Solihull and saw the upcoming new "Discovery". The spy shots are exactly as he described. He told me there would be three Range Rover models, three Discovery models, and three Defender models. Supposedly (and I have read this as well), the new Defender design has been "signed off", but is being extremely guarded. I think it will have some remnants of the notorious DC100, the new line of LRs, and hopefully keep some of the iconic design.
With all that said, this guy also told me that LR's vision is that the Range Rover line is their luxury line, Discovery will be the recreational/active line, and Defender will be the more utilitarian/off-road line. I think they will still stress that all their vehicles are highly capable, but I do believe that the Discovery will become more of an active SUV like the X5, etc. and less of an off-road truck - they will leave that to the Defender.
I have not seen anything reputable about the new Defender line, there are a few renditions, but no spy shots or anything leaked. Like I said, they are keeping things very quiet!