My favorite's always been 1978's "White Youth." It showcases their early, creeping sound, which was distinct from the contemporary crop of UK bands. The best of these bands wanted to sound like The Clash (rip off some reggae riffs, rant about unemployment, and generally try to be Joe Strummer), while the rest simply sped up the Sex Pistols' guitar sound and writhed in their own misery. Crisis, on the other hand, slowed the punk wrecking ball down to a crawl. "White Youth" creeps along with minor guitar notes and a march-step rhythm section. Someone named Phrazer chants out the, well, very Clash-esque lyrics (minus the terse lyricism that made Strummer so brilliant and unique): White youth shouldn't be nazis, they should work with black youth, smash racism, etc. Not very original, but given the context, necessary. The song also stands as an argument against Death in June being nazis, although that's not an argument I care very much about.
"UK '78" is an outraged piece of sneering against the British class system and general late '70s malaise. It's a slightly faster variant on "White Youth," musically: talking-style vocals mixed high, minor note guitar accompaniment, undistinguished drumming.
Anyway, listen to it here. St. Louis' Apop Records released a Crisis discography, with all their material digitally remastered, back in 2005: I recommend buying it, as their other material's good, too. You should be able to find it at the APOP store, here.