Been a while since I visited this thread. Thanks to everyone for your very kind comments.
@ Peter: It's very difficult to pick just one, but I suppose as I use it the most, Phantasm would be my desert island pick.
I use halftones a lot in my work, and being able to make tailor-made vector ones is a huge plus. But Phantasm isn't a one-trick pony, as it is useful for Duotones, Desaturation, Curves, Levels & Exposure.
I don't have the complete set of plugins yet, but MirrorMe is extremely useful and speeds up my workflow, and Vector Scribe makes drawing at least as easy as using Xara's Shape Tool.
I must mention Dynamic Sketch which really makes drawing on a tablet a piece of cake.
To be honest, they are all time-savers and make Illustrator far less of a pain to use.
Bob.