Jamie (in Boston), I like the pictorial guide to confusing look-alike species in The Warbler Guide
("Comparison Species" corresponding to each warbler account and, in addition, pages 512-519 within the "Similar Non-Warbler Species" section).
(Orange-crowned Warbler is shown above.)
In this section, photographs of these look-alike birds feature both Ruby-crowned and Golden-crowned Kinglet, Bushtit, Verdin, Blue-gray Gnatcatcher, Black-Capped Chickadee, Blue-headed (and Plumbeous and Cassin's) Vireo, Yellow-throated Vireo, Red-eyed Vireo, Warbler Vireo, Philadelphia Vireo, Bell's Vireo, Sparrow species, and Eastern Towhee.
This field guide is excellent and recommend it for many other outstanding features that few other field guides host.
Happy Birding On These Last (Precious) Days Of Summer (!), Daniel
(hosts my resume and my "Birding Tours" information....in addition to
birding articles, etc. at the "Birding Links" tab-button)