Visualforce Query Component. Particularly useful for visualforce email templates.

Component_Query.cls

global with sharing class Component_Query {
    global String queryString {get; set;}
    global List<sObject> results {get{
        List<sObject> result = Database.Query(queryString);
        return result;
    } set; }
      
    private static testmethod void contactTest(){
        Contact c = new Contact(lastName = 'apex test contact');
        insert c;
        Test.startTest();
        Component_Query component = new Component_Query();
        component.queryString = 'SELECT id, name FROM Contact WHERE Id = \''+c.id+'\'';
        List<sObject> result = component.results;
        
        System.assertEquals(1,result.size(),'Expected a single contact record');
        System.assertEquals('apex test contact',(String)result.get(0).get('name') );
    }
}

Query.component

<apex:component controller="Component_Query" access="global">
  <apex:attribute name="QueryString" type="String" required="true" access="global" assignTo="{!queryString}"
    description="A valid SOQL query in string form." />
    
    <apex:variable value="{!results}" var="results"/>
    <apex:componentBody />
</apex:component>

Sample_Template

<messaging:emailTemplate subject="Contact Rejection" recipientType="Contact" relatedToType="Contact">
    <messaging:htmlEmailBody >
        <c:Query queryString="SELECT id, (SELECT Comments FROM ProcessSteps) FROM Contact WHERE Id = '{!relatedTo.id}'">
            <apex:repeat value="{!results}" var="result">
                <apex:repeat value="{!result['ProcessSteps']}" var="step">
                    {!step['Comments']}
                </apex:repeat>
            </apex:repeat>
        </c:Query>
    </messaging:htmlEmailBody>
</messaging:emailTemplate>