Herein an interesting selection of unusual and magical creatures that you might wish to entice into being your companion.
The few illustrations provided have a delightfully mediaeval feel to them, but most critters come with just a bald stat block - you will have to look elsewhere for even a text description let alone an image. However if you want a blindheim or a bandersnatch as your faithful companion, this product will get you started... and if you delve through the OGL smallprint at the end, you will find references to where each creature has been published elsewhere in game literature to aid you in further research about your new pet.
Your companion is capable of rising in level as you do, and there's an advancement chart and quite a bit of imformation - including feat and skill - options to help you administer your companion's growth as the campain progresses.
This will certainly give you ideas for other than standard companions, but as only the bare bones are provided you'll have to research those details that will make your companion come to life in your game.