pc power and cooling make great power supplies and that is a great deal. but it depends on what cards you are crossfiring. that would support two cards as far as connectors but if the wattage supports them will depend on what cards.
Don't worry about when a power supply or RAM mentions SLI or CF, it's just marketing and they will support either perfectly fine. There's actually a PC Power & Cooling "Crossfire" edition at 750W - also a marketing ploy and will work with nVidia cards in SLI just fine.
Like bdollar said though, depending on which cards your're looking at, make sure 610W is enough. PCP&P is an excellent brand so good start
Licensing issues determine if a PSU manufacturer can label their unit as SLI or Crossfire certified. It means little.
If a psu has two pci-e connectors, it can handle sli/crossfire for two vga cards that each require one pci-e connector.
If a psu has four pci-e connectors, it can handle sli/crossfire for two vga cards that each require two pci-e connectors.
Quality of the PSU will determine how well the PSU can deliver the advertised power under adverse conditions of load and temperature.
hart140. what kind of video cards are you planning to buy? The Silencer 610W is a great PSU and can handle something like 8800GT SLI or HD 4850 Crossfire.
For something more ambitious (say, HD 4870 Crossfire) get a Corsair 750TX. That combination needs 4 PCI-E connectors, and the 750TX has them. The Silencer 610W only has 2.
These pages show you which PSUs have got official approval from ATI and nVidia. Of course, there are some excellent PSUs that could have been on the list but didn't make it for various reasons (licensing, companies hating each other, etc.). That is, you don't have to restrict your choices to these lists, just use them to see the wattage they recommend.