The seasonal migrations of warblers are exciting, intense, confusing, and over in the blink of an eye. The tools you'll need to survive are a strong neck for looking up, powerful optics, polarized sunglasses, and a phone with TheWarblerGuide.
Every birder is familiar with Princeton's printed edition of the Warbler Guide, but few know about their app. Even if you have the book, TheWarblerGuide is perfect for quick reference and comparison of the warbler species. You can set up your region and season to simplify the listed birds. The images show every angle of the bird possible, including the underside and tail of the bird.
I also love the sound comparison section in TheWarblerGuide , in which you can do an advanced vocal search, based on buzzy quality, number of phrases in a song, upward or downward notes, etc. Bird songs can also be compared to others, which is an incredible feature that helped me identify a Cerulean and Orange-crowned.
This is totally worth the money. Time to go birding!