Just to let the Foundation know I have just donated via the Charities Aid Foundation after selling monitors, keyboards and mice to pi users here.
For everyone else it is very easy to donate to the Raspberry Pi Foundation. just go to the Charities Aid Foundation website - http://www.cafonline.org
and search for Raspberry Pi. Decide how you are going to pay and how much and it is a 2 second job - PayPal is accepted as well as credit and debit cards. Gift Aid in the UK means you include your full name and address and our nice Inland Revenue add a further 25% to the total.