iPod iTunes Store Vouchers

Where can I buy vouchers for iTunes Store where it will be emailed to me ie receive the voucher digitally, within seconds?
I see Best Buy but they seem to only ship physical vouchers? To digital? Anyone have Best Buy experience? Do they offer vouchers via email?

Shanghaichica said:

You can buy them from itunes and it is emailed to you. I bought one from itunes once, it did take about 20 minutes for it to come through though.

Click to expand...

Even without a US credit card? I want to buy iTunes vouchers for US store but with a non-US credit card.