The Arizona Geographic Alliance has created a terrific online collection of geographic resources.
(By the way, did you know that Arizona was the last of the 48-continguous states to be admitted to the Union? Because we're all probably studying different aspects of the Gilded Era when we return from break, including expansion across the Trans-Mississippi West, it might be a good idea to stop and discuss this with your students soon. Ask them to consider: what demographic and geographic features might account for Arizona's admission being the last?)
Go to AGA's homepage and click the green Resources and Links tab, or just click here. There you will see links for resources dealing with geography education, geographic databases, maps, physical geography, geography standards and geographic literacy, and fellowships.
Another useful resource is its list of lesson plans. What made these lessons fun was that they used geographic techniques and concepts to illustrate historical events. Some fun lessons in this collection concerned the Cold War ("It's Not Rocket Science, or is It???"), the electoral college, the Supreme Court's "right to remain silent" case of Miranda v. Arizona, Mormon pioneers, and the Gadsden Purchase.
My favorite resource in this collection, however, is its set of maps. There are other larger map sites you can/should rely on regularly (like d-maps.com for outline maps and the Perry-Castañeda Library Map Collection at the University of Texas at Austin for pretty much everything), but the AGA's collection is still very valuable. First of all, they designed all of the maps in their collection, and the layout they use is very clean and clear. Second, they have a good set of maps showing American territorial expansion (like the maps of the United States in 1803, 1919, 1845, 1848, and 1853). It also has more targeted maps, like the ones about Transportation and Industry in the U.S. in 1860, and the one about the Gadsden Purchase of 1853. Each of these maps is in pdf format which make for excellent printing for our students.