Here in Baltimore we used to have mainly American Crows in the summer and big flocks of (usually very quiet) Fish Crows in the winter, but when the West Nile Virus hammered the American Crows about 15 years ago, the Fish Crows largely replaced them as nesters. The "regular" Crows recovered over time (although I remain convinced that there was some hybridizing going on for a few years, as there were some rather odd caws from adults, back in the 1990s), but there still appears to be only about a 60:40 American:Fish mixture overall during the breeding season, with local variations. Anyway, I just remember the flat, nasal Fish crow "Cah" call by saying that Fish Crows are "the crow that quacks". Interestingly, my wife tells me that the Chinese term for crow means something like that..
Oh, and to avoid the sin of OT-ness, my last lifer was a Chiffchaff on a distressingly curtailed trip to Edinburgh, which featured a damaged Achilles tendon on arrival at Heathrow and subsequent reduced mobility. Luckily, the house we were staying in had a lovely back deck looking over a fairly wild stretch of forest, so at least I could watch the Wood-Pigeons, Jackdaws and Magpies, while hearing all the frustratingly discreet singers so close by. The Chiffchaff, luckily for me, got so wrapped up in its singing that it incautiously let me get a good look at it the day before we left.