FF Yoga Sans by Xavier Dupré is a worthy alternative:
http://www.fontshop.com/fonts/downloads/fontfont/ff_yoga_sans_ot/

I like also Tschichold by Tschichold, revival by Thierry Puyfoulhoux
http://new.myfonts.com/fonts/presencetypo/tschichold/

Linotype's Mundo Sans is gorgeous, as is FF Legato.

Yoga Sans and Legato both look promising. Thanks!

Gotham for approachability
Helvetica for accessibility
Apex Sans for the design factor

You can test my Cabin, it´s free.
http://www.impallari.com/cabin/

Why sans? I usually use seriffed faces in my presentations. Then again I need a lot of weird characters and diacritics – phonetics, uncommon languages, semantics symbols – so there aren’t many decent sans faces that fit my needs. But is there a reason why one should opt for sans over serif in a presentation?

Thanks for the additional suggestions. I'm told that sans serif is more readable, especially at a distance. It seems a good idea to err on the side of more readable, especially if one might encounter unfamiliar presentation conditions. Still, I'm not sure how much of a difference it actually makes. Serif might be fine if one uses reasonable font sizes (which many people don't).

Cool Pablo - thanks for Cabin x

As for sans-serif fonts for presentations, they seem to read better (even at small sizes), and is more informal.
Although, I do alternate sometimes with serif headers/titles/captions/quotes

I would actually argue that serif typefaces are easier to read.
Let us take books for an example, they are all written in a seriffed font. The serif's give fluidity when reading, hence the reason why all books are written in it.

A clean san serif typeface is usually more appropriate for headings and advertisements. Main reason why they are used in most advertisements is for their clean look and appear more modern then serif fonts.

However you did mention that this was a presentation, which I'm assuming entails the use of a projector. If it's a bad projector, you might want to go with san-serif because some lower end projectors cannot project serif's in a clean manor, making it messy and harder to read.

BrettR: That's right, one sometimes does encounter poor-quality projectors, and the other problem is that you sometimes have people sitting far away.

There's a new thread on this topic so I thought I would post with what I concluded. (Not much of a "conclusion" really, just personal preferences of someone who is not a professional designer...)

The most attractive font I found was Ideal Sans. Absolutely beautiful but prohibitively expensive for me: I often need to post public PDFs of my slides and this requires an extra license that starts at $150 per style per year (!!).

Also quite nice: Yoga Sans, Agilita, Sensibility, Calluna Sans, Apex Sans.

Others: Sancoale, Agenda, Whitney, Legato, Tschichold, Mundo Sans.

For me personally, Sensibility or Calluna or just sticking with Gill Sans are currently the top choices. Finally, you might take a look at this thread with many suggestions: Looking for OpenType humanist sans.

No license hazards:
Lapidaria

:-)