Just to clarify.. this is a dekstop not a laptop right??
From what i can find the max resolution of that screen is 1440x900
Depending on your budget i would go for the:
<£100 = HD 5670
£100-150 = HD 5770
>£230 = HD 5850
You should however understand that gaming at below 1680x1050 is relatively dependant upon your CPU...
You might want to look at a cpu upgrade should your socket and/or budget allow for it
If possible post your full system specs and perhaps someone can suggest something
Edit: Sure your moniter isn't the 'H193HQ' ? Either way those three cards are good choices, but that moniter maxes at 1366x768
which just means what i said about CPU is even more relevant to these resolutions