The days of Empidonax as the most difficult-to-identify North American songbirds may be numbered. I have been studying this genus for 17 years and I long ago came to the conclusion that it should be split into four genera. A recent phylogenetic study provides some ammunition for that view. We'll see what the taxonomists have to say. Changing the scientific names of Empidonax spp. won't make them easier to identify, but it will highlight the differences among the groups, and, I think, make the entire assemblage more accessible to the birding public. Meanwhile, they are straightforward to identify by ear, especially if you pay attention to syntax, and that is the mission of this site.
This page is a new portal to materials I have produced over the years to help with field identification of empids and their close kin, the phoebes, pewees, and tufted flycatchers. Here's what's currently available. Some haven't been revised in years, but are still accurate in my opinion.