Artificial Intelligence as a Positive and Negative by Eliezer Yudkowsky and
The Basic AI Drives by Steve Omohundro
Important warnings about the risks of AI. Steve's style is more organized and more likely to convince mainstream researchers. Eliezer deserves more credit for initiating the warnings which led Steve to start worrying about these issues.
The Final Prejudice and
The Cognitive Capacity Argument
Arguments that currently popular attitudes towards age discrimination reflect the same kind of bigotry as 19th century attitudes towards blacks.