My opportunities are linked one to one with contacts. Is there a way when I am doing a contact lookup to just use the contact's email address instead of their name? This is a much more personally identifiable string than the name, especially if we have 6 John Smiths.
If I understand the question correctly, you can add the contact.email field to the "Search Layouts" for the Contact sObject.
Go to Setup->Customize->Contacts->Search Layouts Click "Edit" on the Lookup Dialogs row, and add the email field. What the heck, just add the email field on all the Search Layouts!
What your users will see now is both the Contact Name and the Email... both searchable.
I have found a solution. You can find it here. Summary below. https://help.salesforce.com/HTViewHelpDoc?id=search_enhanced_lookup_enable.htm&language=en_US
Go to Setup->Customize->Search->Search Settings
Here you can select which objects you would like to search every field. This also allows wildcard * searching I believe.