AUTO F/X plug-ins (all of them)
Nik's filters (all of them; pretty useful and amazing stuff)
Flaming Pear (all of them except the free ones, which are a bit... lame)
Andromeda
Alien Skin
KPT (if only they could be updated...)
It would be great if we could have the option to make each and every filter non-destructive (being able to copy/paste them into other objects also, be it individually or as a group of filters. That would be very helpful when dealing with repetitive filter combinarios, for example, while defining Corporate Design standard elements).