Sorry, Angel and the Ape - though now that you mention it, some of the others look fun too.

I take it you've heard Johnny Cash's At Folsom Prison and At San Quentin. Those albums had a huge influence on the outlaw country movement. I also believe you're familiar with some of the artists influenced by outlaw country such as Guy Clark and Townes Van Zandt. While outlaw country is mostly synonymous with Willie, Waylon and Kristofferson, I'd recommend branching out a bit and sample some of the other artists involved.

Longhaired Redneck, David Allan Coe
Juarez, Terry Allen (arguably more progressive country than outlaw, but remarkable nonetheless)
Old Five and Dimers Like Me, Billy Joe Shaver
Whiskey Bent and Hell Bound, Hank Williams, Jr. (kept the movement going in spirit)
Take This Job and Shove It, Johnny Paycheck
Border Affair, Lee Clayton
Bobby Bare Sings Lullabys, Legends and Lies, Bobby Bare
Honky-Tonk Man, Steve Young

There was a revival of sorts in the 2000s, but I figure you probably want to stick with the authentic stuff for the time being. 

Here's five that I think will give you a good feel for the genre and a little peek at its evolution. 

Kristofferson - Kris Kristofferson (1970):  Not exactly outlaw, but the influence is huge.  Kris Kristofferson was THE songwriter of the early 70s.  Absolutely everyone was covering his songs.  Not just country folks, but rock folks, folk folks, adult contemporary folks.  Hell, Percy Sledge and Wilson Pickett were covering his songs.  And he became a legit superstar, becoming, for a while, better known as a movie star than as a singer or songwriter.  Country stars and songs had crossed over before, but not quite like Kristofferson.  

Viva Terlingua - Jerry Jeff Walker (1973):  Still not 100% outlaw...but again the influence is huge.  Two huge influences on the outlaw movement that are largely overlooked are Walker and Bobby Bare.  Walker because of what he did to establish and promote the Texas (particularly Austin) music scene and Bare because he was really the first name country artist to fight back against the Nashville system and gain control of his music.  This album was spontaneous and unpolished and outside the establishment which makes it pretty outlaw.  It also was huge toward accelerating the careers of Guy Clark and Ray Wylie Hubbard as songwriters.  

Honky Tonk Heroes - Waylon Jennings (1973):  This is pure outlaw.  Waylon had been looking for a way to fuse country and rock...and not in the way that the Byrds and Gram Parsons had done it.  He found it in Billy Joe Shavers' songwriting.  This was the counterpoint to the incredibly slick approach that had been dominating Nashville for well over a decade and had almost killed traditional honky-tonk.  I consider this to be ground zero for outlaw country.  

Red Headed Stranger - Willie Nelson (1975):  And this was the album that turned Willie Nelson, songwriter and critical darling in to Willie Nelson: superstar.  It is the zenith of the country concept album and was Willie's first #1 country album.  It is everything that Nashville would never have let happen prior to Bobby Bare, Waylon and the rest fighting for creative control of their records.  Beyond being an incredibly important album it's a damn fine listen.  

Wanted! The Outlaws - Waylon Jennings, Willie Nelson, Jessi Colter, and Tompall Glaser (1976):  When is a compilation album not really a compilation album?  When half the tracks are either previously unreleased or have had new vocals, instrumentals or re-mixes added to them.  This album was a phenomenon.  The first country album to be certified platinum.  Everyone bought it.  Cowboys, rockers, hippies.  It really was huge.  And beyond that, it's a darn good album (parts of it are brilliant).  It's not perfect...but it's super important.