How much do you want to spend ?
£120 +
Corsair AX760
£90 +
EVGA 650W SuperNOVA NEX650G
£50 +
I would recommend the one you already have.
The two £90+ power supplies are excellent with 80+ Gold efficiency awards and are fully modular. To make the decision, you need to decide witch features you want. The EVGA in my opinion looks nicer but the the corsair one has corsair link meaning that you can monitor the usage, efficiency etc.... of your psu through windows. It is also compatible with other corsair link certified products such as H80i and Dominator ram