Most people overlook the room and think problems are caused by their monitors. The listening environment is the first thing that should be addressed before looking into replacing monitors and whatnot. If you haven't "controlled" the environment, it makes life difficult to accurate assess what your monitors are doing.
Monitor positioning in relation to the room is a major factor too. Check the manual for your monitors and there's usually some guidelines about positioning and ideal distance from walls, etc. As an alternative, play a reference CD you know very well and move them around the room until you find the right flat response and imaging.
And if your room does need treatment (they all do), it's not that expensive or difficult to build a couple of bass traps, diffusers, etc. Google for a design for a bass trap, get yourself some rockwool, cloth, make a wooden frame and go for it. Simple positioning of furniture or an extra mattress can help in a pinch too.