try to avoid using RDP, the protocol is terribly in-efficient.
i am working with a customer on just this problem and we have identified the PanoLogic Pano Terminal as one option. it is not a thin client as it has no operating system, it is more or less and extention of a KVM/usb which talks a kind of driver code over tcp/ip and avoids RDP entirely and as such the performance of flash is quite acceptable. the only problem is that it only works in a vdi environment and you must use there VM appliance which acts rather like a broker in setting up the connections and such.
the other choice, that i have yet to try out, is Provision Networks VDI Broker that uses an efficient form of RDP that looks to work quite well. I do not have details but the enhanced protocol is only available when you buy their Connection Broker software.