I also enjoyed "The Birth of a nation" immensly when i first saw it. And it was my introdution to Griffith - not a bad start.
I agree with you, that in 1928 some of the finest silent films were made. It would have really been interesting to see where silents would have developed after that (especially in the US and Germany), but alas, sound came... But maybe there will be a greater production of silent films some day in the future. 
To add to 1928:
A woman of Affairs (great melodrama), White shadows in the South Seas (very interesting anti-imperialism movie), un chien andalou (you know ).