Hmm, if you fps on WoW arent that great than a higher res monitor is gonna be a little tougher. Im thinking that with the current setup a 1440x900 monitor would work nicely, i have a laptop with the same processor and the default res on it is 1440x900, and the 2600 is a MUCH better video card lol. Ill take a look on newegg and post back some of the better monitors i can find.
EDIT: Ok, heres what i found.
1440x900, 19"
Hanns-G- $180 US
http://www.newegg.com/Product/Product.aspx?Item=N82E16824254005
Samsung: $220, This one has a better contrast ratio than the hanns-g monitor, and standing by samsung monitors, i have one and its excellent.
http://www.newegg.com/Product/Product.aspx?Item=N82E16824001259
1680x1050- These monitors could make your framerates suffer somewhat more than a 1440x900 would.
19" Acer X193W $159.99, This is the same size as the above monitors, but higher res so images would look crisper on it. Its got the best bang for the buck of all the 1680x1050 monitors.
http://www.newegg.com/Product/Product.aspx?Item=N82E16824009127
21.6" Samsung 216BW(i have this monitor, its amazing) $250
http://www.newegg.com/Product/Product.aspx?Item=N82E16824001236
21.6" Hanns-G 216DPB Similar in specs to the samsung but a little cheaper, $229
http://www.newegg.com/Product/Product.aspx?Item=N82E16824254028
22" Acer 2216Wbd $220, Ratings on it look good, .4in bigger than the samsung and hanns-g monitors.
http://www.newegg.com/Product/Product.aspx?Item=N82E16824009094
The above monitors look to be some of the better monitors out there. Take a look at the reviews, and decide to yourself whether a dip in fps is worth the higher res. You could of course turn down some of the settings in games for them to run better at a higher res, so take that into consideration. Make sure u read through the reviews and see pros and cons of each monitor, and have a great time when you get your new monitor
-Bomber