easiest way is paypal, if you or your customers use Ebay, then its easy to send and also request money.
the other way is Internet Banking, i have a customer i never ever see, when i've done i send a text and he goes online to his bank account and pays me into my bank. He just needed my Sort Code and Bank Account No., i dont use internet banking but it makes no difference cos it uses BACS i think, where as PayPal just needs an email address