I cannot speak for other ISPs but Zen Internet who I use with Vista is fine. Zen are not the cheapest but you can speak to a real person in Rochdale who can deal with questions in a helpful manner, in my experience.
As far as I understand it the issue is not ISP specific but relates to the modem used to get broadband. Some of the earlier modems and popular with some ISPs do not have drivers which work with Vista. I connect using a modem router through the ethernet port which do not need drivers.