The first way was the arrival of a book I ordered for our Reference Collection, The New York Times: The Complete Front Pages: 1851-2008. The oversized book itself is 300+ front pages from significant days since 1851, and it also comes with every front page contained on a set of DVDs.
Of course, the first thing we did was look up our birthdays, and so far no one was born on a significant day. But we found them in the very easy-to-use, PDF-based, DVDs. No special programs need to be installed, everything worked first time, etc.
Which makes me more comfortable having this book in the Reference Collection - people don't need to take it home if the DVDs work flawlessly on our computers, and the PDFs are ready-formatted to print on 8.5"x11" paper. Reading them is easier electronically when you can zoom in, but the book also comes complete with magnifying lens.
The second way was through Google News search. Not that I was surprised, but I had just never noticed before that Google News added "Archives" links to the left side of the search results page. Clicking into the 1800's, the matches were for-pay links into the Washington Post, but also free full-text links into the NYT. I knew the NYT had made their archive available, but having their articles show up in a context search like this is very useful. Plus, when you click through into the story, there is a link for a PDF version of the original newsprint, which I think qualifies as a primary source.
So, a good day for historical research using the New York Times.