Having a think about bands who had one great album, but their other work never reached the same heights. Could be that their first record was great but subsequent albums were poor, or that they had one standout album in amongst a career of dross.
One that comes to mind for me is Hundred Reasons. Ideas Above Our Station was a classic record, but their albums that came later never seemed to have the same quality. Ideas has great songs, a dreamy feel, a bright, sparkly production and transcends genres, whereas their later stuff seemed to peg them as a post-hardcore genre band and as well as not matching the songwriting quality of Ideas, the production was never on the same par either.
Should be loads of bands out there who've had a brief flare and then faded into obscurity. Care to name some?