First some hybrids:
Violet-crowned x Broad-billed Hummingbird (Amazilia violiceps x Cynanthus latirostris)
Beautifully photographed on Nature Photographers
A stock hybrid:
Golden-winged x Blue-winged Warbler (Vermivora chrysoptera x V. pinus)
Now some vagrants (or thought-they-were-vagrants):
Another Green-breasted Mango (Anthracothorax prevostii), this time in Wisconsin.
What looks like a Black Kite (Milvus migrans) spotted among migrating raptors in Florida, turns out to be a Snail Kite.
What looks like a Common Redstart (Phoenicurus phoenicurus) but is actually a Chickadee.
And many real vagrants:
There is an invasian of asian migrants happening in Alaska this year, as detailed on David Sibley's blog. In addition to the sightings Sibley lists, there have since been -
The first North American Sedge Warbler and the second NA Grey Heron. (you may need to scroll through to find them).