I was looking for a number to word code for apex today and to my disappointment, the only think I could find was a paid app on appexchange http://appexchange.salesforce.com/listingDetail?listingId=a0N300000059Vz6EAE

which I though was ridiculous, so I created my own, its not perfect, but it works and I wanted to share it in the community.

public static string wtn(Decimal i, String curr)
      {
          String text='';
          String bigD='', smallD='';
          Decimal Bn=0, Gn=0, Kn=0, Hn=0, Dn=0, tDn=0, dec=0;
          Integer n=0;
          
          String[] ones = new String[]{'', 'One', 'Two', 'Three', 'Four', 'Five', 'Six', 
            'Seven', 'Eight', 'Nine', 'Ten', 'Eleven', 'Twelve', 'Thirteen', 
            'Fourteen', 'Fifteen', 'Sixteen', 'Seventeen', 'Eightteen', 
            'Nineteen'};
          String[] tens = new String[]{'', 'Twenty', 'Thirty', 'Fourty', 'Fifty', 'Sixty', 
            'Seventy', 'Eigthy', 'Ninety'};

           //More currencies can be added
          if(curr == 'USD'){ bigD='Dollar'; smallD='Cent';}
          else if(curr == 'IRD'){ bigD='Rupiah'; smallD='Sen';}
          
          if((i==null)||(i < 0 )|| (i > 99999999999.99))
              return 'Out of range';
          
          Bn = math.floor(i/100000000); //Billion
          i=i-Bn*100000000;
          Gn = math.floor(i/1000000); //Million
          i=i-Gn*1000000;
          Kn = math.floor(i/1000); //Thousand
          i=i-Kn*1000;
          Dn = math.floor(i/100); //Hundred
          if(Dn ==0)
              tDn =math.floor(i/10);
          else
              tDn =math.floor(math.mod(integer.valueof(i),100)/10);
          dec = math.mod(math.mod(integer.valueof(i*100),100), 100);
          i=i-Dn*100;
     
          n=math.mod(integer.valueof(i),10); //Ones
                   
          if(Bn !=0)
              text = text + wtn(Bn, curr)+ ' Billion ';
          if(Gn !=0)
              text = text + wtn(Gn, curr)+ ' Million ';
          if(Kn !=0)
              text = text + wtn(Kn, curr)+ ' Thousand ';
          if(Dn !=0)
              text = text + wtn(Dn, curr)+ ' Hundred ';                         
          

          if(tDn !=0 || n !=0){
              if(text!='')
                  text = text + ' and ';
              if(tDn <2){
                  text = text + ones[integer.valueof(tDn)*10 + n];
              }else{
                  text = text + tens[integer.valueof(tDn)-1];
                  if(n!=0)
                      text = text + ' - ' + ones[n];
              }
          }
          if(dec !=0){
              text = text +' '+bigD+' and '+ wtn(dec, curr) + ' '+smallD;
          }
          if(text == '')
              text = 'zero';
          
          return text;
      }

so if I call  wtn(250.99,'USD');

I get "Two Hundred and Fifty Dollar and Ninety - Nine Cent"

As I said, the code is not perfect, if there are no decimal numbers, the code doesn't print "Dollar", some space issues etc.

The function can be added in a global class and called in before triggers to fill a text field with the amount in words, or it can be called in a visualforce print and so on.

Hope it helps someone.