You'll find a bunch here. Here is his seminal piece on public goods, three pages long. Here are quotations in appreciation of Samuelson, from Summers, Bernanke, and others. Lucas offered the following:
“Samuelson was the Julia Child of economics, somehow teaching you the basics and giving you the feeling of becoming an insider in a complex culture all at the same time. I loved the Foundations. Like so many others in my cohort, I internalized its view that if I couldn’t formulate a problem in economic theory mathematically, I didn’t know what I was doing. I came to the position that mathematical analysis is not one of many ways of doing economic theory: It is the only way. Economic theory is mathematical analysis. Everything else is just pictures and talk.”
It's mesmerizing to watch the rate at which the Twitter feed is adding messages.
You'll find free pdfs of some of his major articles here.