Being overseas I use Skype for my phone service so I have to pay yearly for my phone number. I used to use gyft.com but they no longer offer Skype. I found http://giftoff.com which does offer Skype gift cards.
My yearly bill came out to $39 on Skype. Giftoff provides a $10 and $25 option. I could have purchased four $10 cards but instead I just went with two $25 cards. I sometimes run into wifi hotspots that accept Skype so having a few extra dollars on my credit is usually good.
The site took about 5 minutes to give me the voucher codes. I had to enter each separately but it went through very quickly. Overall it took about 10 minutes from start to finish.
I recommend Giftoff like the other gift card websites. It mainly offers gift cards for online things like Amazon, Skype, Steam, etc. It is also very Europe centric even though the prices I found was in dollars, they offer euros and pounds and allow you to choose by country.