The International Policy Institute for Counterterrorism, Herzliyah Interdisciplinary Center: www.ict.org.il.
The first of these sites comes from an Israeli university-in-the-making; it offers a wealth of links, short profiles, and on-line articles. Not surprisingly, the perspective is a conservative Israeli one, but that does not detract from the value of much of the material here. Its databases on terrorist attacks are searchable and seem to cover a wide range of organizations, including those outside the Middle East.
The Atlantic, under the editorial leadership of the irascible but able Michael Kelly, has produced some of the more interesting writing on Islamic terrorism, including articles by Bernard Lewis, Peter Bergen, and Reuel Marc Gerecht. Some of the other pieces on this site do not hold up so well, but this is serious journalism of a consistently high order, well worth a visit.