tray.io lets you handle Leads in Salesforce with ease. Using the Salesforce connector, you can find a list of records from Salesforce, using the "Find Records" operation.
The big gotcha
Leads can be converted. Once a lead is converted, you cannot update them in any way, and they are no longer available in the Salesforce interface.
Behind the scenes in the API, Salesforce uses a "Converted" field which is either true or false. You can use this in the Salesforce connector to get a list of leads who haven't been converted yet, for example.
Going a step further, leads can be converted into Contacts, Opportunities, and Accounts. In tray it's possible to get the "ID" of the relevant new converted objects using the "Converted Account ID", "Converted Opportunity ID" and "Converted Contact ID" fields.