Warbler Guy, which birding web site is good to note rare warbler sightings? Rare bird alerts appear at one web site?

Ellie (in Boston), I think you may appreciate:

birdingonthe.net

It hosts ongoing Rare Bird Alert updates from around the country.

So, for example, if I wish to see a summary of rare birds called into the northern California hotline,
I go to this web site.

Here, the latest transcripts from 10/25 - 11/9/14 are featured.

No rare warbler sightings are present in this compendium, but it's still interesting to see reports of

CACKLING GOOSE, FALCATED DUCK, LEWIS'S WOODPECKER, 
TROPICAL KINGBIRD, CLAY-COLORED SPARROW (possible), WHITE-THROATED SPARROW, 
CHESTNUT-COLLARED LONGSPUR, and SNOW BUNTING.