I bought one of these 12 gb dongles (http://www.three.co.uk/_standalone/Device_Detail?content_aid=1220453996371) for my dad (82 years old) to see how he would get on with the internet. He loved it and now has had broadband installed.
So, this PAYG dongle still has over 10.5 gb allowance preloaded and £2.50 credit. It needs to be used by September 2010, and then you can top up as you wish.
Self-installing, use anywhere.
PM me and I'll give you my phone number.