Device to play Blackberry through car stereo

Does anyone have one? I have seen them online for casette players. It looks like a tape with a lead on and you plug the lead into your phone/mp3 player and it plays through your stereo.

They range from a couple of quid to a tenner. Has anyone got one? Can you recommend which one? or another way to do it?

Thanks.
Helen

They sell them in the pound shops.
I cant see the point of spending 15 20 quid on a belkin or griffin branded products..
If you do, try amazon rather than halfords/currys and the like ...

I did have a quick look in there today but couldn't see anything. Will have another look.

Thanks

Helen