1. Cocci (Singular: Coccus): These are spherical or round-shaped bacteria. They can occur individually, in pairs (diplococci), chains (streptococci), clusters (staphylococci), or cubes (sarcinae).

2. Bacilli (Singular: Bacillus): These are rod-shaped bacteria. They can be short and plump, long and slender, or even slightly curved. They can also occur in chains (streptobacilli).

3. Spirilla (Singular: Spirillum): These are spiral-shaped bacteria. They can be rigid and helical (like a corkscrew) or flexible and wavy (like a comma).

While these are the most common shapes, some bacteria have more complex or unusual shapes. For example, some bacteria are filamentous, star-shaped, or even have square shapes.