Do you really need one? at one time I used to have 7 winders. Now, sold 2 while the rest kept in boxes. I now prefer to keep watches in watch boxes.
I may sound ignorant, I tend to agree with meoramri why need a winder? To me is like artificially "wear and tear" the watch faster.
Pardon me if I sound offensive to anyone here.

I agree. Why run the watch when not wearing?
Well, I used to share these view but I am now looking for one due to:
1. Some complications (moon phase, no quick set date) are pain to set and I don't like my watch to display outdated information;
2. I rotate between 3 watches a week (2 for working, 1 to wear for leisure). Sometime watch may run of of reserve if I wear other for 2 consecutive days; and
3. I like winding manual watches (by far my favorite) but I dislike winding those with screw down crown
:p