Sure some people prob know about this but for those that don't . You can order 2 Free T-mobile sim cards from here :

FREE Sim - 2 FREE T-Mobile sims on pay as you go

Mine took about a 5 days to arrive - ordered on monday and was here on friday.

You get £12 of stuff with your first topup, but also £2 was included on each of my sims without a topup or registration.

You seem to be able to order these once every week, they always seem to come, even with same address.

Hope some find this helpful .

Also if you are looking for more sim cards check out the 4 free o2 sims from :

O2 Free Sims