Well okay, not 100% free, but anyone in the UK can buy up to 5 half litre bottles of coke or its other versions (diet, cherry etc) and each label has a code on it giving you a free song on iTunes. You're allowed up to 5 per account so nothing fantastic but heck it's free music worth almost £4.
At this point you're saying, but you have to buy the coke. Yes you do, but even if you don't drink coke, a lot of shops around have a deal of 2 for £X.XX (Tescos is 2 for £1.50, Somerfields is 2 for £1.30, McColls is 2 for £1.29). Well take the price of a song, 79p, and so 2 would cost £1.58 right? So even if you don't drink the coke, you still make a saving!
The song codes expire in December but you can credit your account with them whenever you like 
I did this for The West Wing. Havent done for 24, but that now means I cba to watch it because Its too tense!
I can remember doing this years ago with Friends when it was first being aired. Trouble is it's like reading a book, you get caught in and then two hours later you realise you've not moved or done any work!
It is very tempting to get the second half of 24 series 5 in transcript as I'm just having to wait for the DVDs to be released in November and it's a bit of an agonising wait.