You can be really creative when finding containers to start your seeds. The only requirements are that the container is sterilized, and there are drainage holes in the bottom. I generally just use seed starting trays that I purchase at the garden store, I like to use the larger 3X3 cells so I can allow my plants to grow larger in case the weather isn't quite ready for transplanting.
Here are some suggestions for creative containers you can find around your home:
Make sure to sterilize with a diluted bleach solution (1 part bleach to 9 parts water), and to poke several holes in the bottom of your container for proper drainage!