Same here. They have sucked for a long time. I've seen them like 4 times and I wouldn't go see them now if they paid me. I am happy to say that I saw them when they were still good. I also stopped buying albums after Achtung Baby, but I think the last good stuff was Rattle and Hum. I think the last time I saw them was on the Rattle and Hum tour and that was a great show. I still listen to Boy, October, War, Under a Blood Red Sky, and Unforgettable Fire a lot.
You might want to rent It Might Get Loud also if you haven't seen it. Some cool background on the band and Edge (as well as Jack White and Jimmy Page).