I love my Dremels! I've got two of them, my trusty old 300, and a newer 4000. I got the 4000 because the 300 stopped working, but later I was able to fix it by replacing the speed control & field coils. Although the 4000 is bigger & more powerful, with a greater speed range, my favourite is my 300, as it looks better (IMO) and fits better in my hand. The more useful accessory, I think, is the Multi-chuck, which is far more versatile than the various sized collets.
What about you guys, which is your favourite Dremel drill or accessory?