Lets get going with a new addition, Hot Wheels USS Enterprise from the 2009 movie. As far as I know this hasn't been widely available in the UK, in fact there has been hardly any representations on the new ship on the market.
This is a mix of die-cast metal and plastic. The main hull is metal, while the nacelles and the saucer are plastic.It measures 16 cms in length and is supposed to be 1:50 in scale.
Here it is next to my Corgi Enterprise D. The length of the enterprise D is intended to be 642 meters, while the 2009 Enterprise is somewhere between 610 and 910 meters. The relative sizes of these two models would be about right if the 2009 Enterprise was at the lower end of that scale. Personally I can't picture it being larger than the Enterprise D!