Aren't they all unusual?
Well, perhaps. But in most books the major character or characters are human or, in the case of science fiction and fantasy, human-ish. Over the years, however, there have been a number of exceptions:
1. An animal. To my knowledge, the first non-human protagonist in a major novel was Black Beauty. Watership Down has its wonderful rabbits and cartoons are well known for animal protagonists - most people instantly recognize Scooby Doo. For those of us over a certain age Tom and Jerry and Sylvester and Tweety are great comic duos. One could also include the muppets. Or the wonderful dogs of Disney's 'Lady and the Tramp'.
2. A ship. Michael F. Flynn's "The Wreck of the River of Stars" uses the ship's artificial intelligence as a major character, but he's not the first. Anne McCaffrey's 'brainships' are an arguable example (transplanted human intelligence). And, of course, one could put the iconic computer HAL 9000 in this category. Let's not forget the Doctor's TARDIS. Not all ships as characters are intelligent, though - both the Millennium Falcon and Star Trek's Enterprise are quite memorable characters despite having no intelligence of their own.
3. The planet Earth - David Brin's interesting environmental novel called simply 'Earth' essentially has the earth itself as a protagonist.
4. A dragon or other fantastic creature - Anne McCaffrey's Pern is notable for how real her dragons are and the trend was picked up by other authors. Novik's Temeraire is simply one of the most fun characters around. Mercedes Lackey is particularly fond of fantastic creatures as characters - including the horse-like Companions, well-realized gryphons and an interesting take on dragons as non-sentient, trainable animals.
5. A robot. To most people these days, Star Trek's Data is the most recognizable humanoid robot, but he's an homage to Asimov's robots. R. Daneel Olivaw is one of the best-realized robot characters ever. On a less serious note we have Wall-E and, before that, Number 5.
6. A computer. Not all fictional computer characters are mobile. HAL 9000 has already been mentioned, but there's also Portal's GladOS and Heinlein's fascinating Mycroft.
7. A place. Edward Rutherfurd has written an interesting series of historical novels in which the protagonist is a place, usually a city. (These are well worth a read if you have any interest in history at all).
Can anyone think of any more?