'Measure of a Man' is a brilliant episode; definately in my TNG Top 10. As people are already saying, Picard's speeches in favour of Data were riviting, and of course poor 'toaster' Data is just a stand in for slavery, or racism. The court room setting may now seem a little obvious, but it was still excellent.
I also love 'The Offspring.' It wasn't a classic like 'Measure' was, but the reocurring theme of android sentience really had more of an emotional kick. Lal malfunctioning made me cry, especially if the episode is watched after 'Measure.'