These spring to mind:
Visage - Fade To Grey
Walking In My Shoes - Depeche Mode
Doctor Who Theme - Delia Derbyshire & The BBC Radiophonic Workshop
Technically the last is Music Concrete rather than a synth... but hey!
Wow, five pages, and no one's mentioned Ultravox, who were early entrants in the Euro synth-pop sweepstakes...
Members contributed heavily to the 'Visage' album, and while, yes, they were heavily influenced by Kraftwerk(the Chuck Berry's of synth), Bowie, Roxy, and Brian Eno(who produced their first album), they were mercilessly ripped off by Gary Numan(the irony being that UV keyboardist Billie Currie played on Numan's hit "Cars"), and this track in particular was pilfered quite a bit by Berlin for their "Metro" hit(I was in a band that opened for them over 30 years ago, and they so much as told me this).
Gary 'fesses up here...
Here's my favorite UV track from the original line up...
Delia Derbyshire was a fascinating and visionary aural sculptor, plus she had that sexy librarian thing going on. The original Dr. Who theme was done in the very early 60's with oscillators, proto-sampling(recordings of musical glass) and tape loop manipulation, no synths(didn't exist yet!), and was an influence on Paul McCartney, especially the loops used on "Tomorrow Never Knows", and if you listen closely, you'll hear where Pink Floyd got a lot of the freak out part(before the drums explode and the groove kicks in with the slide guitar)on "One Of These Days"...
If you want to know more(she died tragically from cancer...)