i'm quite pleased with my introductory level Alesis M 520's. dirt-cheap @ €200 a pair & real nice and clear to get a balanced mix on. only downside is that they sound "too good", with that i mean: excellent clarity to get a decently balanced mix of your tracks yes, but they blatantly fail to point out some obvious resonance issues here & there.
on the plus side, they're fantastic to just listen to music on. a friend has a pair of the yamaha's supergroover mentioned and tbh those are just built to make a critical mix on, they point out & exagerate every little flaw in the sound. the downside of those monitors is that they're not very pleasant to actually listen to. very harsh resonating sound overall imo.