Your graphics card seems capable of handling large resolutions.
In a nutshell: go buy a square peg for your square hole. In a hopefully-not-too-complicated-explanation: Check and see what your GC's maximum resolution is (Asus's website says it's 2048 X 1536 for your card), and then go invest in a monitor that suits that max resolution (monitors, besides their physical screen size, list what their maximum supported resolutions are and often what their "maximum-performance at maximum-supported-resolution is). The only (sane) reason you would need a better graphics card is if you got some uber (expensive) monitor and then couldn't utilize that new uber monitor's maximum resolution because your GC can't supply it (sure you could force the square peg into the round hole, but it won't look purty).
I have two monitors, a 19" samsung LCD and a 20" widescreen samsung LCD (I'm a fan of samsung LCDs, both at work and home, quality/reliability/lifetime

you can find them on sale for a nice price too sometimes). I use the 20"W as my main, and I must say, at an arms-length away it is awesome for gaming and entertainment. My 19" was honestly too tall for my comfort as my main monitor at that distance (it was my main monitor for ~3 years before I got the 20"W). Off and to the side my 19" is perfect (it still works perfectly, I just wanted 1) a widescreen and 2) an excuse to hook up two monitors to my computer

). I was thinking about getting a 22"W or a 24"W but at the time there was a great sale going on the 20"W I got, and now that I've gotten comforitable with it maybe the 22"W (certainly the 24"W) at an arms-length away would have the same "too tall" feeling I had with my 19" as my main at that distance.
Good luck with your monitor shopping.