The high school students in our home school co-op just read a lesson from the Notgrass World History Curriculum about music history. Here is a selection of 10 pieces from the composers featured in the chapter. I haven't personally listened to all of these. Some of them are full-length, and the students might want to just listen to several minutes. I hope they will be inspired to look up more pieces for these composers and for other composers in these musical periods. I will try to compile a list of 20th century links soon.
For more information, be sure to visit these classical music sites:
Baroque
Classical
Romantic