How can I just prepay say 500 dollars on my itunes account, so that I dont need to have multiple transactions on my credit card...?

Hello DilipVenkat,

Welcome to the Apple Support Communities. If you want to have a purchase iTunes Gift Cards to have credit on your account, just purchase an iTunes Gift Card at your local Apple Online Store or through iTunes. Store.

iTunes: Sending iTunes Gifts

http://support.apple.com/kb/ht2736

iTunes Store: How to redeem a code

http://support.apple.com/kb/HT1574

Regards,

-Norm G.

Can u redeem code immediately w online purchase or do u have to wait for card to come in mail?