Battlefleet Gothic is still going
afaik.
And the classes of ships is like it is nowadays.
Frigate, Destroyer, Cruiser(Light then heavy), Battleship.
There are loads of variatons between each end of the classes but that's theorder of power (I think, not too sure about Frigates and Destroyers)
Automatically Appended Next Post: http://wh40k.lexicanum.com/wiki/Imperial_Navy
This should help.