I planned to show the photographs on my MacBook, which has recently been refurbished, but hasn't had iPhoto reinstalled on it. Running late, I didn't have time to install it as planned. As a last resort, I thought I'd just show the photos using Quick Look and scroll through them in full screen.
When I eventually got round to showing off my photos (you know, that rather drowsy time just after dinner), I realized that Quick Look won't let you scroll through items when in full screen,
Well, to say the least, with hundreds of photos to get through, people already getting bored, my finger hurting from scrolling and my wife giving me the look that says "I told you so," I began to wish I had made the time to reinstall iPhoto. There was no internet access either, so I couldn't even download something like Picasa.
At that point my cousin strolled into the room and said, "That must be taking you ages, why don't you just do a slideshow using Preview?" He then selected all the photos in the folder, right clicked and selected 'Open With Preview.' With the Preview app open, he selected 'View' from the menu bar and then 'Slideshow.' It was that simple.
Thankfully, I was able to leave the photos to display themselves. People could watch as much or as little as they wanted, when they felt like it (the way such photo exhibitions should be!).
You can check out more things to do with Preview at this Apple support page.
Update: A few bright commenters have pointed out that you can, in fact, do a slideshow using Quick Look. First, select more than one photo, then hit the space bar or the Quick Look button. By selecting more than one photo the slideshow options will appear in the Quick Look window. Thanks!