I often use a prototype to present ideas. Having an interactive example, as opposed to a flat wireframe is very useful to explain even simple interactions. To your question, these types of models don't work well in a slideshow. I occasionally link to a prototype from within a slideshow to connect it with other thoughts that are best presented in slides.

I've had great success with showing a prototype and also providing printouts of each screen to the meeting attendees. I encourage them to annotate the printouts and I collect them afterwards to review. Some people are much more comfortable writing ideas down instead of sharing them aloud with a group.

As other presentations go, HumanCentric gave a Prezi presentation at World Usability Day here in NC a few weeks back. I really liked how this showed overall process and literally zoomed into smaller-scale details along the way. I'm not sure if I'll ever use this format, but I was impressed with it. http://prezi.com/rkikqfae3o-r/

As with anything the message should inform the presentation medium. I don't think there's a one-size-fits-all solution to this one.

I've been playing around with Prezi for product presentations, and I'm pretty sure that it would be great to structure ideas, principles and even navigation in a really WOW way.

That being said, when it comes to prototypes there's nothing like a piece of paper - provided it's still 'big' concepts rather than detail. If you're into the detail already, then electronic prototypes win with me.

There are lots of ways to present UX and I hope to see interesting ideas in comments.

I'd like to say a little about the paper. If you have to present design to a small group of people paper prototypes may work perfect (especially during some early stages of design process). A great advantage is that everybody likes to write notes and corrections just on your prototype. So it encourages discussion and helps you to gain more useful feedback.

The visual design of your interface also looks perfect being printed so I'd recommend to present it on paper rather then on a screen. In my experience it worked excellent.

I always start out with paper and pencil. When I'm ready to share my designs with a larger audience, I recreate them in a sketchy prototyping tool (I use iPlotz) and create a low-fi but interactive prototype.

This really helps us to visualize potential holes in the design, and really get a feel for how the app will actually work. I use this with both our engineering team and customers and have found it effective for both.

iPlotz allows for commenting, so when users click through/view the designs, they can add comments as they come up.

I tend to use this as it's a fairly quick way to enable sharing with remote users without having to fuss with scanning sheets of paper.

For mid-project workshops, I usually show only short slideshows to start the discussions. In my experience, they are too formal and people are less likely to give feedback.

Interactive prototypes (ie. Axure) are much better and I often add big bubbles with questions and comments to guide the workshop.

Lately, I have been using Balsamiq. However, my answer is: Whatever is easiest, quickest, cheapest that still gets the point across and makes people go "Wow, that would be cool!"

I find Visio is pretty bad for that.