You could get a third-party GPU cooler (will have to get back to you about a few if you follow this option).
Or, you can get another 4670. Similar alternatives would be a nVidia GT 240 or ATI HD 5670.
But for your usage, you don't need anything near as powerful & can easily make do with something half the prices of the above GPUs. A few examples are:
nVidia-based (start at £22 +del): click here
ATI-based (start at £25 +del): click here
All of those in the links should be able to run 2 monitors, but if you'd like to confirm it with the one you go for, just ask. G