Open Sensor Search is a not a portal and not a catolog, but your one stop shop if you want to find sensor data on the web.
Although it is not a catalog, it can be used as one with its web service interface for managing sensor catalogues and sensor descriptions. It is based on the OGC discussion paper 10-171 (Download at OGC) and presents a quite pragmatic solution that may serve as the basis for further discussion and development.
These details are provided for information only. No information here is legal advice and should not be used as such.