I'm going to start with the latter two instances first.
First on the list is Lady Antebellum. For their first three albums, Lady Antebellum made solid country or pop-influenced-country music. They were far from traditionalists, but they had country roots in their music. Since then, they've released two albums that have moved into more and more pop and less and less country, becoming almost exclusively pop at many points, with their last two singles, "Bartender" and "Freestyle" being absolutely unbearable to listen to. However, off of their first album, this song, "One Day You Will," was a particular highlight.
Next up is Kenny Chesney. Up until his most first Greatest Hits CD, Chesney also made decent country music. He even had several songs that were *gasp* very very good. Sure, that collection also contained the abysmal "She Thinks My Tractor's Sexy," but to be honest, if such a motif hadn't become what it has in mainstream country, the song would be a novelty song worth laughing with instead of at. After that Greatest Hits album though, he went on his island vacation and has seemingly never returned. However, Greatest Hits also included this gem, "What I Need to Do," which is very reminiscent of George Strait's "If I Know Me." He still puts out a decent song every now and then, but overall, this song shows Chesney in an element where he wasn't just an island boy.
So much for the half-sell-outs. From here out, it's the big-guns. Those who have shown in the past they can make good country music, but have abandoned that completely in favor of a brand of music that flat out gives country music a bad name, at least in the mainstream.
First, Toby Keith. In a similar vein to Kenny Chesney, up until his first Greatest Hits CD, Keith put out some really strong material. Then he entered his "How Do You Like Me Now" era and just become as brash as he could be, with each progressive album becoming more and more about being a drinker who's out to kick the ass of anybody who dares to disagree with him. Every so often, he'll sprinkle on a decent song, like "American Soldier" or "Cryin' For Me," but the Keith who made the albums that contributed to that first greatest hits album is long gone. Here's one of his earlier songs, off of his Blue Moon album, "She's Perfect.:
Jerrod Niemann put out one really decent album before moving away from country music and into an era of music which includes songs like "Donkey" and "Drink to That All Night." We can all still look back though at his second single "What Do You Want" and remind ourselves that this guy wasn't always a tool.
Jason Aldean. Jason, Jason, Jason. What are we going to do with you? You've drifted so far away. "Dirt Road Anthem"? "1994"? Fucking "Burnin' It Down"? This is so far away from what you're capable off. Remember this song, "Back In This Cigarette" off of your second album? Go back to making songs like this, Jason, and maybe gain back some of the respect you've lost.
Yes, even Brantley Gilbert once made music that didn't make him sound like a complete tool. Here was an early song that wasn't on any of his albums. It was a song called "You Promised," and Gilbert actually shows he's got some vocal ability. Sure, he's not an award winning singer, but he's also not the asshole singing "Bottoms Up" or "Small Town Throwdown."
Granted, most of these artists have gone so far in the wrong direction that they're unlikely to turn back. But good songs should be respected, no matter who they're coming from. And these songs, despite the artists they are from, show that there was once something more to them.