The Cordless Action Controller by Logitech is a great wireless alternative to the standard PS2 1st party wired contollers. Unlike some third party controllers, the Logitech controller feels quite similar Sony's controller and does not try to provide any of the gimmiky features that bog done other controllers. The range on this controller is excellent, and it does not experience any noticable lag; I could be on the other side of the room and play Gitaroo Man and never miss a note. Battery life is also surprisingly good considering that the controller allows vibration; one pair should last around 15 hours of gameplay.
However, this controller still does fully have the feel of a 1st party controller. I've had some of the buttons stick momentarily. This has never interfered with gameplay as the buttons click back on their own but it can be irritating nonetheless. The adapter also forces the slim PS2's to incline a little bit because it is slightly too big.
These slight problems should not deter anyone from getting this controller, however, as its convenience and long battery life make it a worthwhile investment. I haven't used a first party controller in months and have absolutely no desire to go back.