...most bands are

edit: most GREAT bands are...

It's hard to restrict it just to ones you could hear on the radio today, as that's basically modern bands plus ~50-odd well known bands from the past.

But if you want a list of musicians/bands/artists playing over 25 yrs ago who still sound fresh and original today, I think it'd be a very long list....

Velvet Underground
Frank Zappa
John Cale
David Byrne/Talking Heads
Gil Scott Heron
Beefheart
.... Actually I've started writing this now and realised I can't be bothered filling in the other 20 or 30 people I was gonna put here. Basically, the point I'm making is that there's lots of them but you probably wouldn't hear many on the radio now. I think there are also plenty of bands whose music has aged well (i.e. some stuff you hear on the radio from way back that still sound contemporary and interesting, like some early stones stuff, Lou Reed circa Transformer, that sort of thing), and a lot of folks whose music is "timeless" in a way that the genre they played in hasn't really evolved as such since their days, such as the later 1950s Chicago blues performers (Buddy Guy, Otis Rush, Freddie King etc), the great soul singers like Otis Redding, Sam Cooke (OK he'd say he was gospel but I'd say soul!), etc etc.

The Clash are a pretty good example though, always had a soft spot for bands in the punk era that fed off the overall "feel" of it whilst ploughing their own furrow, and I think the Clash fit neatly into that category with their kind of public school/reggae/african influenced take on the whole thing. London Calling is just a brilliant song.