Here is a really useful source of archival data made available for re-analysis, class projects, testing new hypotheses, etc.:
This is the ICPSR, a consortium for data archiving and management. It hosts an enormous collection of well annotated scientific data. Member institutions get full access, but a large proportion of the hosted data is freely available to the public. Most data sets have code books and can be downloaded in multiple formats.
I (Bob) learned about this from a presentation by Nora Dunbar at Northern Arizona Univerity given at the 2016 Society for Teaching Psychology conference. She gave an overview of how she uses this resource for undergrad teaching and as a source for really fantastic constructive replication projects formmasters students. Some of here students presented their projects, and it was really impressive the types of interesting questions they could ask and answer with archival data. I plan on using ICPSR and imagine many others will find this a useful resource.