UK

Three has the best coverage and PAYG, no contract or residency requirements is £20 for the USB modem plus £10/1GB, £15/3GB, £35/7GB. Alternatively, you can get a one-month contract (possibly requiring stupid UK proof of residency documents?) for £15/5GB, plus £10 for a dongle.

http://threestore.three.co.uk/broadband/

Alternatively, T-Mobile dongle lets you use wi-fi on West Coast main line trains and in Starbucks for free. We haggled them down on the phone from £15/month to £10/month for 3GB.