What about invoices?

Originally Posted by Robson Of course, you could just send them a paypal invoice? Nice and simple.

True, but it's possible that the other party don't intend to pay you via PayPal

I think, especailly as far as web design / development is concerned, cheque/cash or bank transfer is probably the best method of payment. That is, of course, providing the client is reasonably local (within your country, at least).

I think it would be good practice to issue an invoice (and a receipt), yes. It always useful (for you and the other person/business) to have a paper based record of the transaction which has taken place - mostly for tax reasons, but it's certainly can't do any harm anyway.