The event that brought the US into WWII was the bombing of Pearl Harbor. Here's a video containing President Roosevelt's Pearl Harbor Address also known as "a date that will live in infamy" speech.
Snag Films offers three films about the bombing of Pearl Harbor including this one hosted by Tom Brokaw.
The National Parks Service offers lesson plans about Pearl Harbor and the USS Arizona.
Google Earth has a layer that features aerial imagery of 35 European cities bombed during WWII. Among these cities are Warsaw, Lyon, Naples, and Stuttgart. To view this imagery and compare it to modern imagery, locate a city in Google Earth then use the timeline slider to view the historical imagery.
The Science and Technology of WWII provides students and teachers with lesson plans, timelines, essays, images, and learning activities about the scientific and technological developments that took place during WWII. The darkroom section of the website contains thirteen categories of images of WWII scientific and technology developments. The timeline on the website allows students to explore the scientific, technological, and political steps in the development of the atomic bomb. The learning activities section of The Science and Technology of WWII gives students the opportunity to learn about and send coded messages.
Conflict History is a good example of what can be accomplished by mixing Google Maps with a timeline. Conflict History provides a timeline at the bottom of a Google Map. Select a range of dates on the timeline and placemarks representing conflicts appear on the map. For example, if you select the years 1941-1945, every conflict that happened around the world in those years appears on the map. For major conflicts such as World War II, individual campaigns and battles appear on the map.
The World at War is an interactive timeline about FDR's decisions during WWII. Click on any of the key decisions listed to learn more about those decisions. The decisions are interspersed amongst other key events of WWII. None of the events are terribly detailed, but the timeline does provide a nice general overview.
World War Two: Europe and North Africa 1939-1945 Map is a narrated overview of the main events in those areas. What I like about this video is that it provides visual, geographic context for the events discussed by the narrator. Watch the video below.
World War Two: Asia and the Pacific 1941-1945 Map uses the same concept as the video above to illustrate the Pacific theater of WWII.
The BBC's World Wars In-depth series contains some great audio, visual, animated, and text resources for learning about WWII from start to finish. WWII In-depth contains a timeline overview of the war. From there you can jump-off in a number of directions to explore details about WWII.