With Campaigns there's a couple of options for marketing. Here's few videos:

how to import lead from a trade show.

Also leads 3rd part mass email tools can be used to mail leads & contacts and then use lead capture to connect to a campaign where during conversion a lead is combined with an existing contact to create a new opportunity.

IContact is an app that use the campaign member list to send mass emails and then store the results back in salesforce, but some have raised the issue that it takes up alot of space.

Thanks

Eric Stephenson