Samsung R780 and second monitor

Hi,

I've bought a R780 and now I want a second monitor.
The laptop screen resolution is 1600 x 900.
I can only find 20; monitors at this resolution and I'd like something a little bigger i.e.
22; or 24;.

How can I tell what resoutions will be supported on a larger monitor with this laptop's graphics capability?

I don't want to commit to a monitor only to find that the display is not sharp because there's a mis-match between laptop graphics and monitor capabilities.