Here's my lists (for the United States). The birds aren't in any particular order:
Favorites I've Seen
This list probably changes day-to-day.
1. Greater Prairie-Chicken
Tympanuchus cupido
This charismatic symbol of the tallgrass prairie is now sadly limited to tiny fragments and remnants across its formerly wide range. The one time I saw them was on a lek at Buena Vista Grasslands, the largest prairie left east of the Mississippi River. After seeing that amazing display, there was no way it couldn't make it onto the list. I know I said these aren't in any order but this probably does deserve the number one spot.
2. Great Tit
Parus major
I'm fascinated by introduced species, and this one intrigues me because of its small, localized population in Sheboygan, Wisconsin, only about an hour's drive away from where I live (it's the only population of the species in North America). The population has been going strong for nearly two decades now, yet even most birders in area don't know they exist. These birds truly are beautiful, too, especially in winter against the snow. I'm jealous of you Europeans who get to see one every day, this bird is tough for me to track down and usually requires special effort to see.
3. Whooping Crane
Grus americana
Most birders go to Texas to see these, and often aren't aware that the second largest breeding population of this species is in Wisconsin. Here they are quite easy to see in the right places and often can be viewed at close range. The chicks are super cute, and birders who go to Texas don't get to see those!
4. Pine Grosbeak
Pinicola enucleator
Beautiful bird with truly underrated beauty. This is a boreal species that occasionally irrupts into northern Wisconsin. I've never seen it in Wisconsin, but I did see them at Sax-Zim Bog in northern Minnesota. The landscape was covered in freshly-fallen snow and hoarfrost that day, meaning there was basically no color anywhere except for on conifer trees and these birds, which made quite the striking view! My favorite photo I've ever taken was of one of these birds, which I'll get around to uploading later.
5. Sanderling
Calidris alba
This is the cutest bird (that's a fact). Watching them skitter over the beach on a wavy day is extremely entertaining, I could watch it all day.
6. Gray Hawk
Buteo plagiatus
Early in my birding career (I was probably somewhere around 11), my dad took a business trip to Arizona and on some time off got me a hat from the gift shop at a local nature center. The hat had a Gray Hawk on it, which is an endangered species in the US, and within the US is found only in Arizona and Texas. This hat became a symbol to me of my desire to travel and see birds, and I still wear this now-battered hat practically everywhere I go. Seeing this hawk in the wild in Arizona earlier this year was an absolute thrill. I was, of course, wearing the hat at the time.
7. Phainopepla
Phainopepla nitens
This wasn't a species I had any particular desire to see when I saw in Arizona for the first time back in spring. But after I saw one for the first time I fell in love with this species. Their "we-weedle-ah!" call is full of character and gives a beautiful sound to the otherwise very quiet Sonoran Desert. The fact that they are specialists on two entirely different habitats at different times of the year is very unique, as well.
8. Rivoli's Hummingbird
Eugenes fulgens
An impressively large hummingbird I viewed from less than a foot away. How could it not make the list?
9. Parasitic Jaegar
Stercorarius parasiticus
The shows this bird puts on are extremely fun to watch, as it dives at gull at weird angles in an attempt to get them to drop the food that're carrying. I've never been to the ocean so I've only seen this bird on Lake Superior, but I think that almost adds to the fun of seeing this bird, and my photos show Duluth in the background!
10. Common Loon
Gavia immer
I imagine most of you reading this will have only encountered this species in their wintering grounds or in migration. You have no idea how much you're missing. Of all the bird species I've seen, this one just feels the most wild. It lives on far northern lakes, surrounded by trees, and their haunting call gives off a unique sense of wonder and eeriness. While I see the argument for calling this bird either "Common Loon" or "Great Northern Diver", I think only the name "Great Northern Loon" can truly represent what seeing and hearing this bird on its breeding grounds is truly like.
11. Great Gray Owl
Strix nebulosa
I saw this giant owl comically sitting on the point of a Black Spruce just before it was too dark to see. Need I say more?
12. Rosy-faced Lovebird
Agapornis roseicollis
I just have to include another introduced bird. They're just so interesting! I've never kept lovebirds, but I loved seeing them at zoos at pet stores when I saw a little kid. They were probably my favorite bird for a while. Never did I think I would see them in the wild. Yet there they are, in the middle of Phoenix!
13. Black-capped Chickadee
Poecile atricapillus
I see these every day but this list would feel incomplete without them. These birds are almost as cute as Sanderlings and have just as much personality. They never sit still and are always bouncing through the trees and shrubs and making fun noises. "Chicka-dee-dee-dee"!
14. Vermilion Flycatcher
Pyrocephalus obscurus
I doubt there is a birder alive who has seen this bird and wouldn't put it on this list. It's the reddest bird there is, and you can tell a cardinal I said that. It's so striking against the greens and browns of their riparian habitat!
15. Gray Jay
Perisoreus canadensis
Yeah, that's the name.
16. Gambel's Quail
This was among the birds I was most excited for in Arizona and it did not disappoint. They're super cute and their calls are so fun and they travel in big flocks on the desert floor and they're so fun to watch and - let's just say there's a lot of reasons to love these little guys.
17. Winter Wren
Troglodytes hiemalis
I would love to give this spot to all the wrens I've seen (it's one of my favorite bird families) but this one gets the top spot for its ridiculously long song in relation to size. How can it do that?
18. Dark-eyed Junco
Junco hyemalis
Here in Wisconsin we get the Slate-colored Junco and only in winter. The bird is extremely abundant then, though, and the first junco of the season in late September always makes me so happy! In Arizona I saw several other subspecies (Gray-headed, Oregon, and Pink-sided) and they were cool too. I almost gave this spot to Yellow-eyed Junco, which is just as cool as the Dark-eyed.
19. Northern Jacana
Jacana spinosa
Only a rare vagrant to the US, I saw the long-staying individual in Tucson that was there for nearly a year. It happened to be my 300th life bird and I can't think of a better #300.
20. Warblers (sorry I couldn't pick one) Parulidae sp.
Every May, Wisconsin forests are filled with these little Neotropical migrants. They fill the forest with color and song for a few weeks as the leaves come in. I thought long and hard about which one to pick, but I just couldn't decide. But my favorites are Blackburnian, Cape May, Black-throated Blue, Magnolia, and Chestnut-sided.
Top I want to see
Obviously many, many more, as I'm not well-traveled (I've only been in the Midwest and Arizona).
1. California Condor
Gymnogyps californianus (so mad I missed this one at the Grand Canyon!)
2. Elegant Trogon
Trogon elegans
3. Roseate Spoonbill
Platalea ajaja
4. Snail Kite
Rostrhamus sociabilis
5. Scissor-tailed Flycatcher
Tyrannus forficatus
6. Iiwi
Drepanis coccinea
7. Boreal Chickadee
Poecile hudsonicus
8. Piping Plover
Charadrius melodus
9. Black Skimmer
Rynchops niger
10. Pin-tailed Whydah
Vidua macroura
11. Canyon Wren
Catherpes mexicanus
12. Kirtland's Warbler
Setophaga kirtlandii
13. Indian Peafowl
Pavo cristatus
14. Blue-and-yellow Macaw
Ara ararauna
15. Green Jay
Cyanocorax luxuosus
And many, many more...