The following were recorded over my home in Elkins Park, PA during August. All identifications are presumptive.
Least Bittern (3.24am, early Aug)
Upland Sandpiper (3.26am, mid-Aug).
Black-billed Cuckoo (4.32am, early Aug).
Chestnut-sided Warbler, a relatively low fine buzz (12.13am, mid-Aug).
Compare with the higher, lazier buzz of Yellow/Blackburnian/Blackpoll/Connecticut Warbler. Most likely a Yellow based on the date (3.05am, early Aug).
The Common Yellowthroat call is usually easily separable as a low electric buzz, but calls are variable and not always double banded, as here (2.55am, mid-Aug).
Here's a nice comparison between American Redstart and Black-and-white Warbler, The calls have a similar shape but the sound is quite different (mid-Aug).
Canada Warbler can sound a bit like American Redstart, but is very different on the sonogram (3.24am, early Aug).
The Cape May Warbler call is sharp, high and usually descending (5.33am, mid-Aug).
Shortly before dawn, some warblers call frequently as they descend, similar to the vocal behavior of Catharus thrushes. Ovenbirds with a Mourning Warbler calling, a few Bobolinks in the background at the end (5.41am, mid-Aug).
Mourning Warbler is the lower call