Statistical analysis of terrorist groups' longevity, aims, methods and successes reveal that groups are self-contradictory and self-sabotaging, generally ineffective; common stereotypes like terrorists being poor or ultra-skilled are false. Superficially appealing counter-examples are discussed and rejected. Data on motivations and the dissolution of terrorist groups are brought into play and the surprising conclusion reached: terrorism is a form of socialization or status-seeking.
http://www.gwern.net/Terrorism%20is%20not%20about%20Terror
Hm. I'm far from an expert, and it could well be that there are ten times as many anonymous attacks, but off the top of my head I think of WTC '93, the Millenium plot, 9/11, London trains, Madrid trains, Israel suicide bombings, Munich massacre, Iraq beheadings, USS Cole, bombings of US embassies.
Not off the top of my head: Golden Mosque bombing, Tamil Tigers numerous bombings, IRA-related terrorism, etc. Scanning through this I find many more terrorist attacks that were done with a clear political or propaganda purpose.
A good heuristic I use when I'm tempted to write comments such as these: "The plural of anecdote is not data!"
Note also that attacks for a reason may well be more memorable than anonymous attacks.