I am looking to acheive the same result. I have a button which I've added to my Custom Object which then grabs all of the selected records and displays those selected records. The next step is what i'm having trouble with and that is grabbing the list of campaigns - showing that list and then being able to add the custom object records ContactIds to the campaign as members.

I feel as though if I could only get this list of campaigs to show here, that I'd be able to grab the informatiom I need to write the code to add them.

Here is my controller:
 

public with sharing class MerchantLeadController {
    private final Merchant_Lead__c merchantLead;
    private final Campaign campaignsList;

    public MerchantLeadController(ApexPages.StandardSetController controller) {

        //merchantLead = [SELECT Id, Name, Contact__c FROM Merchant_Lead__c
        //WHERE Id = :ApexPages.currentPage().getParameters().get('id')];

        List<Merchant_Lead__c> mlId = (List<Merchant_Lead__c>) controller.getSelected();
        List<Merchant_Lead__c> merchantLead = [SELECT id, Contact__c FROM Merchant_Lead__c WHERE id IN :mlId];

        List<Campaign> campaignsList = [SELECT Name FROM Campaign WHERE IsActive = true];

    }

    public Merchant_Lead__c getMerchantLead() {
        return merchantLead;
    }

    public Campaign getCampaign() {
        return campaignsList;
    }

    public PageReference save() {
        update merchantLead;
        return null;
    }
}

I'm not 100% clear on how to structure it to get what im looking for....I can reference the !campaign in my Visualforce page but the contents of the query are not showing.  Here is my VF page:
 

<apex:page standardController="Merchant_Lead__c" tabStyle="Merchant_Lead__c" recordSetVar="Merchant_Lead__c" Extensions="MerchantLeadController" >
    <style>
        #col1,#col2{width:100%;display:inline-block;valign:top;}
    </style>
    <apex:form >
        <div id="col1">
            <apex:pageblock title="Campaign List Management">
                <apex:pageblockSection title="Merchant Leads">
                   <apex:pageBlockTable value="{!Merchant_Lead__c}" var="a">
                      <apex:column value="{!a.name}"/>
                    </apex:pageBlockTable>
                </apex:pageblockSection>
                <apex:pageblockSection title="Campaigns">
                   <apex:pageBlockTable value="{!Campaign}" var="b">
                      <apex:column value="{!b.name}"/>
                    </apex:pageBlockTable>
                </apex:pageblockSection>
                <apex:pageblockButtons >
                    <apex:commandButton value="Save"/>
                </apex:pageblockButtons>
            </apex:pageblock>
        </div>
        <!--<div id="col2">
            <apex:pageblock title="">
                Show Current Campaigns and their stats?
            </apex:pageblock>
        </div>-->       
    </apex:form>
</apex:page>