Bob Geldof of the Boomtown Rats
I figured "forgotten" as people that were yuge at a point in time then kind of disappeared from the music scene. Not so much as some of the one hit wonders.
I wanted to stay away from a status achieved and stick with a where the heck did they go model, I only put Hole in as a tongue in cheek post and they would fall more as a one hit wonder for me.I suppose there is a difference between the prototypical "one-hit-wonder" and a "forgotten" artist. However, I'd say that once an artist reaches that elusive iconic status, I have a hard time labeling them as "forgotten." Hole is a good example of your definition (other than Courtney showing up on TMZ every couple months for something weird). They had two giant albums and then kind of fizzled.
But, and these aren't meant to start an argument, just my peculiar 2 cents:
Bolan - He's a legacy guy, especially across the pond. Bowie followed his lead (one of the only times you can say that about Bowie). I love his stuff but he's probably the least talented guitarist to ever have a Gibson signature guitar (at a steep price) http://www.musiciansfriend.com/guitars/gibson-custom-marc-bolan-aged-les-paul-electric-guitar?source=3WWRWXG9&gclid=CLG60YOsy80CFQMQaQodFVwFDg&kwid=dynamicsearchads-adid^75067330940-device^c-campaign^[ADL]+[Non@ADL4Brand]+[US]+[Enhanced]+Test+@ADL4+Keywordless-account^Musicians+Friend+@ADL4+Google+@ADL4+US-adgroup^Dynamic+Search+Ad+Group
Syd - I'm probably biased on this one because I'm one of the few that actually enjoys Madcap Laughs. He burned out but I don't know if he'll ever be forgotten. Piper was revolutionary and his "antics" provided a lot of material for the Gilmour era songs.
Peter Gabriel - Led the massively influential prog-era Genesis, followed it up with arguably the biggest album of the early MTV era, and provided the blueprint for late '80s/early '90s production and instrumentation.
Talking Heads - The most recognizable American post-punk band with a decade worth of great albums.