I second that - RAMBUS it still too overpriced for the performance it gives you. Look under the mainboards articles on this site, Tom has written a few on RAMBUS.
Only reason you'd need to buy it is for multiprocesser servers. Same goes with ECC RAM. Your motherboard also has to support it and all of your RAM would have to be ECC. I remember reading somewhere ECC is slighly slower ~ 2-5% loss in performance.