Head over to the Coupon Center of your jfu account and click "special offers". If it's still available, you should see a $15 offer for iTunes. Basically, you get $15 off when you spend at least $50 on iTunes gift cards!
Now, if you want to get experimental, try buying a multi-pack, since they are offering an instant 15% discount on iTunes multi-packs. You'll have to have at least $50 AFTER the discount though, so try buying (2) 3-card packs of $10 cards. That would mean your total would be $51 before the $15 off.
could should get $60 in iTunes gift cards for just $36!
That would also give you (6) $10 cards, which would be great for gift giving or stocking stuffers!
(Thanks, Mashup Mom!)