Best Practice for Lead Management After Conversion

Historically we had not used Leads, only Contacts.

Now that we have deployed Sugar Market we are using Leads.

As Leads are converted, what do you guys do with them so they don't simply clutter up the Leads tab?

So much of the information in the Lead record doesn't make it over to the Contact record anyway, I just don't know what value the Lead record has after conversion.

You thoughts would be appreciated.