Television's guitarist Tom Verlaine was a major influence on Edge's guitar style, according to the beanied one himself.
the Ramones and the Clash also seem to be influences, and Bono has talked about loving the Velvet Underground and I think the Stooges before, so perhaps you could count those in. Nowadays they're listening to BRMC and stuff, so who knows...
actually there was that Zoo Radio thing which I thought was interesting - Edge, Adam and Larry playing their favourite songs. Of course, favourite don't necessarily mean influences, but...