Here is some of the websites that you may want to consider:
There are tens of active bike registry systems, so better to chose the one that is more active in your local area.
registeration of the bike is something that is better to do before you get your bike stolen since in many cases, you would be provided with some kind of bike tag that indicates your bike registration and kind of deter the bike theft before it get stolen. however you still can register your stolen bike in stolen bike registeries after the crime; Here are some examples:
The other option you have is the possibility to use GPS trackers and locate the position of your bike using this technology.
There are currently several GPS trackers in market:
SPYBIKE (Hidden in bike light and headset)
BikeSPIKE(Hidden under bottle cage)
SHYSPY (Hidden Inside seat tube)