We get a large number of leads, often they already exist as a contact and want to be able to do the following:

We go through an initial follow up with the lead and then when we wish to convert we want to select an existing contact to update or link the contact to an existing account.

It would be great to be able to look up that an account or contact already exists at the lead screen.  Could use email address or "similar" company name as an alert.

Main question, how do I effectively get leads into existing contacts.