1971's Rock On album was, by my lights, one of the best albums of the "classic rock" era, but it didn't even crack the Billboard "top 100."  One occasionally hears this hard rock number, but little else from this well-crafted album featuring Steve Marriott and Peter Frampton.  After this album, Humble Pie enjoyed its most successful years in the U.S. with Rockin' the Fillmore and (without Frampton) Smokin', but I still am of the opinion that Rock On is their best album.  Here's one lesser-known song for a taste:

And here's another one of my favorites: