Kottke has a good post today outlining some of the notable magazine and newspaper archives that are available online:
In past few years, several prominent US magazines and newspapers have begun to offer their extensive archives online and on DVD. In some cases, this includes material dating back to the 1850s. Collectively it is an incredible record of recent human history, the ideas, people, and events that have shaped our country and world as recorded by writers, photographers, editors, illustrators, advertisers, and designers who lived through those times.
For instance, Sports Illustrated just opened up the SI Vault, with full-text of every issue. I worked at SI from 1994-1999, and you can now see everything I wrote for them.
I'll throw in one more good archive: Wired, where you can read full text of every issue of the mag.