How can I associate Leads from a list with both a Lead Source and Campaign but not run a list more than once?

Whether you're using a Salesforce list uploading tool or a tool from an AppExchange partner such as RingLead's Declone Mass List, you can always create a column within your Excel spreadsheet titled "Lead Source" and populate it with the Lead Source you would like to associate with each record in your list.  You can then use Salesforce's Lead or Contact list uploader to create new Leads and/or Contacts in your database and then later search for duplicates and merge any that you may find.  A Campaign can be associated by either uploading your list to the Campaign or assigning members to a Campaign after using the general Lead or Contact upload tool.

RingLead has also created a list upload service which will not only de-dupe your list against your entire database of Leads, Contacts, and Accounts, but it will also associate the campaign when chosen, create new Contacts within existing Accounts, associate same company Leads, support lead assignment rules, and assign a task to inform a sales person when one of their Leads/Contacts responds to a new campaign or marketing tactic.  An added benefit is the flexibility it will provide you to either overwrite an existing Lead Source with the new one from your list, update a blank Lead Source field, or append the new Lead Source into a task while allowing you to keep the existing Lead Source intact.  All of this in just one uploading of a list.