I bought a 1 G Vodafone dongle for ?30 which includes ?15 top up. It works like Skype credit you have to use it within 6 months to keep the credit otherwise you will lose it. Have used it at various hotels recently with excellent results. Only works in the UK and bought it from Maplin. Used about ?2.50 over a weekend which is brilliant value compared to the ?15 a day vouchers hotels want to charge.
As I am off to France tomorrow I have bought the Vodafone 3g dongle, cost ?25, includes the ?15 for one month top up, should work in Europe, pay as you go, but expires after 1 month. I am planning on leaving it with my brother for him to continue to use after I return home. Hopefully I will let you know how I get on with it on Saturday.