How should I list presentations given at workshops on my CV?
Any position that builds your career or profession has a rightful place on your CV. It sounds like your workshop leading experience has done that, so I would vote to put it on. To be clear, I'm assuming that by "presentations in workshops" you mean that you led a workshop where participants worked through something (since "workshops" are typically not lectures my field--I could be mistaken about your field), which I'll refer to as "workshops facilitated" 

The question of where to categorize it is more complex I think, and it depends on the nature of the workshops. I think there are three main options:

1. "Workshops facilitated" sub-heading under a "Conferences" or "Presentations" Category 

If you think the skills you developed and displayed in facilitating the workshops is similar to the skills developed and displayed in participating in conferences, and your workshops were about research of a caliber you would present at a conference. 

2. "Workshops facilitated" sub-heading under a "Teaching Experience" category

If the workshops you facilitated were more focused on general topics than your own independent research. 

3. "Workshops facilitated" as its own category

If the workshops you've facilitated do not fall neatly into one of the two categories above. If the workshops you've facilitated are very distinct from either of these options, or if you've facilitated a mixture of workshops, I think it's reasonable to put them in their own category. You could even have sub-headings of "Research-focused workshops", "Introductory workshops" or "pedagogical workshops", etc.