I can't remember where I got the last one from but I can't seem to find anywhere where I can get a £15 iTunes gift card without having to wait for it to come through the post. Apple and Paypal both only offer £25 and up.
I just go to the App Store, then select Featuees and send gift I then send myself a £15 voucher. Works fine
I think they send out promo codes or serials of sort that get sent to your email if you gift it to yourself.
I've done it a few times, just had an email saying to reclaim my gift etc. Works a treat There used to be a few sites in the UK where you could get cheap itunes vouchers, eg £25 for a £30 voucher. Think they've all been taken down, still get the odd cheap one on ebay
You can get cheaper ones from cd keys.... I have had a few. Get an extra 5% off with a Facebook code (you don't have to like them, there is a page where you can add any fake email address then it shows you code) http://www.hotukdeals.com/deals/itunes-gift-card-codes-50-for-41-99-25-for-21-99-cd-keys-plus-2-quidco-2233410
