Apex Controller:

public  class acctTemplt
{
    public Id accountId {get;set;}
    public List<Opportunity> getopptys()
    {
        List<Opportunity> oppty;
        oppty = [SELECT Name, StageName FROM Opportunity WHERE Accountid =: accountId];
        return oppty;
    }
}

Component:

Name:OpptyList

<apex:component controller="acctTemplt" access="global">
    <apex:attribute name="AcctId" type="Id" description="Id of the account" assignTo="{!accountId}"/>
    <table border = "2" cellspacing = "5">
        <tr>
            <td>Opportunity Name</td>
            <td>Opportunity Stage</td>                
        </tr>
        <apex:repeat value="{!opptys}" var="o">
        <tr>
            <td>{!o.Name}</td>
            <td>{!o.StageName}</td>              
        </tr>
        </apex:repeat>        
    </table>
</apex:component> 

Visualforce Email template:

<messaging:emailTemplate subject="List of opportunity" recipientType="User" relatedToType="Account">
    <messaging:htmlEmailBody >
    Hi,<br/>
    Below is the list of opportunities for your account {!relatedTo.Name}.<br/><br/>
    <c:OpptyList AcctId="{!relatedTo.Id}" /><br/><br/>
    <b>Regards,</b><br/>
    {!recipient.FirstName}
    </messaging:htmlEmailBody>
</messaging:emailTemplate>