Michelle,
What you want is a report called "Leads by Original Source Info." This report will show the count of leads from every list import as well as some opportunity metrics.
To create this:
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Create a new report of the type "Lead Performance"
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Click on Setup
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Change the attribute "Group Leads By" to "Original Source Info"
This report will show you the forms and lists that brought in all leads. By default it shows the last 30 days.