As it was showed in the topic linked beneath, should be a good improvement to show methods of payment in every invoice, and linked to payment methods. Also should be default payment when enter the amount of money.
Also it would be an extra improvement to decide the default kind of payment for invoice or/and for customer.
And also showed in the report templates (pdf - html).
Please do not discuss feature requests in this forum as we have a special board for feature requests and improvements. This is the link to the discussed topic: http://goo.gl/ghpLKh
Please share your thoughts there.