I absolutely love FastStone Image Viewer and I highly highly recommend it. It is free, does a great job and displaying photos in full screen, has extra features like batch renaming, batch converting, batch resizing, basic photo adjustments etc..., you can view up to 4 photos at the same time full screen to compare them, and it is very flexible and configurable to your likings. I recommend setting it's file associations to all the picture formats so that photos will automatically open in full-screen mode (via FastStone) whenever you double click on them. You can also choose whether to show the photo's name in full-screen view or not. That is really helpful if you are going through a bunch of photos and want to write down which ones you will use for something.
The mini version is FastStone MaxView. That only has the photo viewing features and nothing else.
Both come in regular free installation version and in free stand-alone, portable versions to carry on your USB thumb drive.
Here is the link. They also have other freeware like ScreenCapture and so on.
http://www.faststone.org/
So, can you tell I love this program? I can't believe it is totally free - no adware, no spyware or anything like that. I does not organize your photos, but if what you are looking for is a photo VIEWER then this is definitely the way to go.
PS - one more thing..... while viewing a photo in full-screen mode, you can move your mouse to each of the four ends of your screen and different menus with options will pop up for quick access. Okay, okay, I'll stop. I just think it is a great program.