What’s the best place to buy PlayStation Network Cards?
If you want to get PSN card codes or PSN subscriptions (US accounts with US Dollars only) delivered to your email, try Offgamers:
Web of Trust gives them a 4 out of 5 rating, so they're a pretty reputable site.
SlickDeals.net occasionally has info on places selling various cards (PSN, XBox Live, Steam, etc) for less than face value. I've seen some go as far as 20% off ($40 for a $50 card). You can set up email alerts on the site to be notified of specific deals you are looking for.
Amazon, eBay, Sony's website, grocery stores where they're sold...
Apart from occasional deals, you're not going to find a bunch of different, competing prices for them. A card worth $10 is going to sell for $10.
You can get PSN cards from the below link -