It's appropriate that I begin a series of postings about educational software with one of the classical heavy hitters of the genre. I think that practically everybody from my generation has played some version of Oregon Trail at least once in their lives. Personally, my all time favorite is the old school Apple II version. 
For the uninitiated, Oregon trail is a simulation where the player takes the role of a pioneer and must navigate from Independence Missouri to the Willamette Valley and arrive with at least one traveler still alive. The player has the choice of choosing a pioneer with one of several backgrounds; each occupation having particular benefits. For instance, starting as a doctor results in a much higher beginning cash balance, while a school teacher (as in real life) starts out very poor.
Throughout the journey, the player must make important decisions, such as what supplies to purchase, and in what amount, what paths to take, when to hunt or forage for food, how hard to push your wagon team, and the ever popular choice to attempt to ford the river or wait for an Indian guide.
The game is excellent for conveying such learning objectives as planning for unforeseen consequences and cause and effect relationships. It can also be a collaborative effort where students must vote on each important decision, much like settlers may have done on the real Oregon trail.
The game also teaches valuable information along the trail about historical landmarks and in later versions, gives students the opportunity to talk to other settlers about their experiences and learn a little more about the trail, and the locations they visit.
Curiously, it was a little hard tracking down a current copy of Oregon Trail, as MECC, the original publisher appears to have closed down in january of 1999. The Learning Company now holds the lucrative license to this piece of educational nostalgia.
For teachers looking to justify using this in the classroom, let your administrators know that it fulfills several of the ISTE's Educational Technology Standards for Students (NETS).
Creativity and Innovation:
c. use models and simulations to explore complex systems and issues
Critical Thinking, Problem Solving, and Decision Making
Students use critical thinking skills to plan and conduct research, manage projects, solve problems, and make informed decisions using appropriate digital tools and resources. Students:
a. identify and define authentic problems and significant questions for investigation.
b. plan and manage activities to develop a solution or complete a project.
c. collect and analyze data to identify solutions and/or make informed decisions.
d. use multiple processes and diverse perspectives to explore alternative solutions.
Not too shabby for a $20 program that was originally designed over 25 years ago.
For teachers on a budget, there are several free versions floating around which offer the authentic Apple II version of the game in a emulated environment right in your browser. While the original version doesn't offer the same depth as newer versions, it's just as valuable today and the NETS standards are still addressed.
Consider it the perfect addition to a US history unit. Older students will appreciate it just as much as the younger ones and they might even learn something.
Virtual Apple Game
The Facebook Game
Purchase Information
The Oregon Trail
Grades: 3+
Ages: 9+
Operating System: Windows + Mac
Price: $19.99
Website