Try googling free sims, although you'll have to wait for the postman tho.
I've had mine for more years than I can think of and topping up when I need to/want to is handy.
Oh and Orange are offering free texts if you top up by £10 and they also have a competition running at the moment where if you win, you get £20 credit added to your phone:)
I have recently got a giffgaff sim card. I put £10.00 on it every month and it gives me 250 mins( to landlines and mobiles), unlimited texts and unlimited access to the internet. Good value I think.