Completed inspired by re-watching** Walk the Line**.
I was vaguely aware of Johnny Cash as I was growing up, but I don’t recall that we ever actually owned any albums. I’m not interested in any of the gospel stuff.
iTunes gives me a staggering number of albums to buy, greatest hits, classic hits, best of, very best of (surely superior), essential, legend, etc.
Any Cash fans that can give me a recommendation? 
The only one I have is At Folsom Prison, so I’m not an expert, but I think that one is generally considered as his definitive work. This is the basic version - there are bigger expanded ones, too.
Live at Folsom and Live at San Quentin are essential classic Johnny Cash albums. They are better than any best of collection you will find, get them both. You also want to check out the American albums which are full of Johnny covering songs and making them sound like he wrote them. These are the albums where his more recent hits like “hurt” and “one” came from. I like American 1, 3 and 4 best, but all are good.
The Essential Johnny Cash - 2002
or
The Legend of Johnny Cash - 2005
The Legend of Johnny Cash Vol. II - 2006
If you’re gonna get just one I agree with (Live) At Folsom Prison.
When I was a kid, Johnny Cash had a TV variety show. It wasn’t really ‘my kind of music’, but I watched it anyway. Something about Johnny Cash, I guess. I forgot about him for a couple of decades, except when I’d hear him occasionally. He just kept popping up on the radio. There was a TV show called Space: Above And Beyond where a guy falls into a black hole or something, and he played his beloved Johnny Cash music. That got me thinking about The Man In Black, and I picked up a collection of his music from 1955-1983 (see below). Then Hurt came out, and it was so much better than NIN’s version. So now these are the Johnny Cash collections I have:
American Recordings
American IV: The Man Comes Around
Unchained
The Essential Johnny Cash (1955-1983)
Is the sound quality good on Folsom Prison? I think I might just buy that this weekend myself, never having owned any Johnny albums before.
The sound quality is excellent, particularly on the newer remastered version. It’s live, but it was always intended to be recorded. Though I beg everyone to not dismiss “Live at San Quentin”, it’s less famous but every bit as good as Folsom Prison.
BTW: I think The Man Who Couldn’t Cry on American Recordings is hilarious.
I concur with the American Recordings and the live albums, but you really need a collection of his early Sun Records recordings, too. That way you have early, middle and late and with a discography like his you need them. All three eras are very different and all are equally great.
Good point.
This looks like a great collection, but I don’t own it personally so I can’t say anything other than that it looks great.
If anyone has a specific recommendation for an early collection I would love to hear it.
Thanks for your responses! Sounds like one album will not be enough, but I’m going to start with Folsom.
Me too. Let’s compare!
ETA: Thanks for starting this thread. I was shopping for a CD last week for my daughter, and ended up browsing some Johnny Cash stuff and was thinking “I bet I’d like this. But what to buy?”
Are we allowed to compare our johnnies in here?
Get Folsom and San Quentin first, but make this your third.
mmm
You tell me, Johnny. 
Will do.
My favorite Cash is Unearthed – 79 tracks encompassing his changing style throughout his life. The packaging is almost as brilliant as the music. The discs are in brown paper sleeves in an album, just like grandma’s 78’s.
I thought I was keeping up but I see that there are more American recordings I don’t own. I need more Cash (and more cash).
The opening of Dark as the Dungeon sends shivers down my spine!
Unearthed only covers the American Recordings period, from about 1994 till his death. That said, I agree that it’s a stunning collection. One of the discs is a gospel album, though, so the OP may not want it.
There’s a 4-disc version of The Legend Of Johnny Cash that covers his entire career, and is a pretty good overview, but I’ll agree with most of the other posters and say that Folsom Prison and San Quentin are the best starting points.
The 3-disc box set of Love God Murder is a fantastic collection that organizes each album by a theme but covers a broad span of his career. I’d recommend all 3 (they’re also sold individually), but if you had to choose one, go with Murder.