Yes, I also want to add my accolades to the Celebration of 'On The Border'. I also love this album. It is my 2nd favorite overall, right after their true masterpiece, Desperado. But, I think sometimes On The Border gets somewhat lost in the shuffle of their other great albums (Like Desperado, Hotel California, and their later albums), and doesn't seem to get the recognition it deserves as a great album itself. I really like every song on the album, there are no weak tracks, but some of the standouts for me are Already Gone (perhaps their best pure rocker?), James Dean, Good Day in Hell, My Man, Ol' 55, and Best of My Love. My only complaint - sure wish they would have included Bernie's lost rocker, 'Georgia Peach' on the album (instead it seems lost forever).
Just a couple other comments about what others have said. First, I think the notion that this was the album where The Eagles moved away from country-rock and became a more straight-forward rock band is way overstated, and not really supported by the music itself. Although the addition of Felder certainly added some scintillating guitar leads to Already Gone (and would later lead to a harder rock edge), overall this album is no more 'Rockin' or any less 'country' than its predecessor. Desperado, although often cited for it's 'country' sound, is really not very country at all. More Bluegrass influence yes, but that's different from 'country'. Desperado contained 2 of their hardest rockin' songs in Outlaw Man and Out of Control. Yes, The Eagles 'Rocked Out' just fine even before Felder and Walsh came along. And the songs on On The Border have just as much 'country' influence as Desperado. Midnight Flyer is an all-out Bluegrass stomper (as was Twenty-One on Desperado), and Pedal Steel guitar (an obvious 'country' influence) is featured on at least 3 other songs. In fact, this is a classic album that fully utilizes their unique 'country-rock' style to the fullest. That is one of the reasons it is so great. I also would disagree that it is inherently more upbeat than previous albums. More Uptempo, yes, and perhaps a bit brighter sound mix, but not really more upbeat, in that the themes and issues of the songs are still quite dark and ominous (but we like that, don't we?).
Anyway, a great album, and great partly because of it's superb mix of rock and country influences throughout.