I use two smaller screens these days instead of one larger one, it's more useful from a development point of view than it is for game playing though. I've heard reasonably good things about Dells *monitors* (but the rest of their kit). Iiyama, Viewsonic, LG, all the main brands provide decent kit. Generally stay away from Acer, Asus et al.
One thing to note though, if you do go the dual screen route, make sure they're the same models so you don't struggle with colour calibration, which can be a real pain without spending money on a calibration kit; even though monitors are supposed to use an industry standard they vary wildly from manufacturer to manufacturer.
