Pretty good data-only SIM card. I usually get a few and just cycle through them as I need them, they can be cut down to micro-sim size for the iPad. You basically get up to 3GB of data that does not expire for 3 months. No contract, just PAYG. Throw the SIM away at the end of three months/3GB and get another! :-)
Start date is from *first use* so you can buy them in advance and stick them in a drawer. The amazon price seems to bounce up and down a bit, but £9 is pretty good for zero-faff SIM deal.