I created a visual email template that works with:
--a custom object called OT__c,
--a visualforce component called OTComponente, and
--an apex class called OTPresupuesto.

My problem is when I receive the email, it has some fields in blank, I think it has to do with the id of the custom object.
Specifically this part:

From OT__c Where Id=:System.currentPagereference().getParameters().get('Id')

when I put in my apex class just the "From OT__c" without specifying my Id, the email I recieve looks like this:
 

Nuestra Ref.:
Sucursal:
Fecha:24/08/2015

Total a Pagar:0,00
Saldo a Pagar:0,00 
Sub Total:0,00
Nombre:
RUC:
Name:

Gracias por elegir Maker!
Saludos Cordiales,
El equipo de Makerxmail

and when I put the "From OT__c Where Id=:System.currentPagereference().getParameters().get('Id')" the email looks like this (​the component doesn't even appear):

Nuestra Ref.:
Sucursal:
Fecha:24/08/2015 


Gracias por elegir Maker!
Saludos Cordiales,
El equipo de Makerxmail

this is my apex class OTPresupuesto

public with sharing class OTPresupuesto {

    public List<fact> factList{get;set;}
      
    //Constructor  
    public OTPresupuesto() {
        this.factList = new List<fact>();
        for(OT__c ot2 :[Select Name, Nombre_de_la_Cuenta__c, Sub_Total__c, RUC__c,
                        Total_a_Pagar__c,Saldo_a_Pagar__c
                        From OT__c Where Id=:System.currentPagereference().getParameters().get('Id')  LIMIT 1])
        {
            factList.add(new fact(ot2));
        }
        
    }       
    
    public class fact{                   
        public OT__c OT{get; set;}                  
        public string saldoPagar {get; set;}
        public string subTotal {get; set;}
        public string totalPagar {get; set;}
                   
        public fact(OT__c ot2){                           
            this.OT = ot2;                           
            this.saldoPagar= NumberToSpanishWords.convertToEU(ot2.Saldo_a_Pagar__c);  
            this.subTotal= NumberToSpanishWords.convertToEU(ot2.Sub_Total__c);
            this.totalPagar= NumberToSpanishWords.convertToEU(ot2.Total_a_Pagar__c);
        }   
    }     
}

and my visual component OTComponente

<apex:component controller="OTPresupuesto" access="global">
        
        <apex:repeat var="as" value="{!factList}">               
                Total a Pagar: <apex:outputText value="{!as.totalPagar}"/><br/>
                Saldo a Pagar: <apex:outputText value="{!as.saldoPagar}"/> <br/> 
                Sub Total: <apex:outputText value="{!as.subTotal}"/><br/> 
                Nombre: <apex:outputText value="{!as.OT.Nombre_de_la_Cuenta__c}"/><br/>
                RUC: <apex:outputText value="{!as.OT.RUC__c}"/>  <br/>
                Name: <apex:outputText value="{!as.OT.Name}"/>   <br/>   
        </apex:repeat>    
</apex:component>

this is my visual email template called EnvioPresupTemaplate

<messaging:emailTemplate subject="RE: {!relatedTo.Asunto_email__c}" recipientType="User" relatedToType="OT__c">
<messaging:htmlEmailBody >       
    <br/>
    <b>Nuestra Ref.:</b><apex:outputText value="{!relatedTo.Name}"/><br/>
    
    Sucursal:<apex:outputField value="{!relatedTo.Sucursal__c}"/><br/> 
    Fecha:<apex:outputField value="{!relatedTo.Fecha__c}"/><br/>
    
    <br/><c:OTComponente />
    <br/>
    <br/>
    Gracias por elegir Maker!<br/>
    Saludos Cordiales,<br/>
    El equipo de Makerxmail
</messaging:htmlEmailBody>
</messaging:emailTemplate>