Kate Bush, definitely. Run, don’t walk, and grab some of her stuff right now.
Genesis are fairly unique, even in prog circles. King Crimson, Gentle Giant and Spock’s Beard are all good suggestions, however.
Have you heard Exposure by Robert Fripp or Sacred Songs by Daryl Hall? These were recorded alongside Gabriel’s second solo album and they all sound very similar, especially Hall’s album, believe it or not. All three were produced by Fripp.
Another left-field suggestion: Alice Cooper’s Welcome to My Nightmare seems to exist in some grey area between Gabriel’s first solo album and Pink Floyd’s The Wall, with an extra dose of vaudeville camp. Producer Bob Ezrin is the common thread here.
Next suggestion: My Life in the Bush of Ghosts by Brian Eno and David Byrne. Closer to Talking Heads circa Remain in Light, but still reminiscent of Gabriel’s more experimental soundtrack work.
Midnight Oil’s 10-1 is pretty much a direct descendant of Gabriel’s third solo album and so has that “In the Air Tonight”/“Mama” atmosphere pervading it.
Stewart Copeland’s solo output, such as The Rhythmatist, is also highly recommended. He’s the drummer from The Police, and he’s worked with Gabriel on occasion. Think worldbeat. And if you’re choosy, Sting can be excellent, too.
Finally, it may be worth looking into Steven Wilson. It’s not exactly Gabriel or Genesis, but he is heavily influenced by Pink Floyd, King Crimson, Peter Gabriel and Kate Bush, among others.