For RDP - I've been using TeamViewer. I had it on my iPhone over a year ago before I switched, and I have it now on my Thunderbolt. It works fantastically - only downfall is that the free version leaves a message on the target machine every time you disconnect saying "this was the free version, if you are using this for corporate use, please pay for it..." blah blah blah. It's annoying because if I connect to my home HTPC and then disconnect. It leaves that message up on the screen, and kind of messes with my wife the next time she tries to use the HTPC.
So I might look into this "Splashtop" you all seem to be raving about just to see if it doesn't leave that warning message behind. But other than that, I have been MORE than happy with TeamViewer.