In cooperation with Hearst, Google Books has posted 106 years of "Popular Mechanics" back issues. If you're running any kind of pulp game, including "Call of Cthulhu", this is a goldmine of material just waiting to be mined. The inspirational power of decades of "cutting edge" technology from the early part of this century is simply amazing. Airships! Land leviathans! Steam juggernauts! Spaceships!
Update: It's even better than I thought. They also added the entire run of "Popular Science" going back to 1870.