Just in town today and saw these and had to get one !!
£39.99 gets you a modem + your first 1GB of usage - after that its £15 per 1GB
What is best - get this- unlike everyone else who puts a time limit of the use (i.e. use it within month) you can take as long as you want to eat through the 1GB.
By my reckoning 1GB @ £15 will last me around 6 weeks !!! Thats cheap
Vodafone are also reported as the best speeds for mobile broadband.