At MMOGA there are currently i.e.:
[UK] Playstation PLUS - PSN PLUS Card - 365 days - 57,81$ instead of 71,64$
[DE] PSN Card 20 Euro - Playstation Network Credit 23,87$ instead of 25,14$
[US] Playstation Network Card PSN Key 20 Dollar 20,10$ instead of 27,64$
[CH] Playstation Network Card 35 CHF 41,47$ instead of 44,00$
and many more...
The code will be sent to your email address within 5-10 minutes after receipt of payment. Even without a credit card, you can easily top up your PlayStation Network balance.
Enjoy :)