Existing data sets that are derived from large-scale scientific projects are typically very easy to access and can be readily incorporated into an inquiry-based interactive learning activity appropriate for introductory courses.

For example, in an interactive activity, students can be asked to carefully inspect the figure above (click figure to enlarge it) and answer such questions as:

Also, see general discussion on How to Use Data for relevant ideas.

Many data sets are presented in tabular form and can be easily imported into a spreadsheet program like Excel. For example, one activity has students import data from the US Historical Climate Network into Excel to help students learn about local climate change and about using Excel's statistical functions. 
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Interactive JAVA or Macromedia based links allow students to easily access global data sets. Here are two examples of interactive data sites. The IRI/LDEO Climate Data Library also has easy to use data analysis and manipulation tools available.

Geographic Information Systems (GIS) also provide an easy to use integrated environment of data, data visualization, and analysis tools. Mapping Our World is a low cost package with GIS lessons from ESRI, the makers of ArcView.

There are many available links to good quality data sets appropriate for introductory geoscience education.