Pour 1/2 cup baking soda into a bowl. Add just enough liquid soap to make a creamy paste. Spread mixture on the flat side of 1/2 of a lemon, and scrub. The lemon acts as a sponge and leaves a natural citrus scent. Use a damp rag or sponge to wipe away any residue. You'll find the paste will stay moist for a few hours.
Vinegar is a great all-purpose cleaner; use it straight for tough jobs or dilute it with water. Tea-tree oil is a natural fungicide and can help disinfect surfaces -- mix 2 teaspoons with 2 cups water. To whiten stained tiles or grout, use a mixture of 1/2 cup hydrogen peroxide to 1 cup water. All of these solutions can be sprayed onto a surface, allowed to dry, then wiped with a damp cloth.
Vinegar works well on soap scum and mineral deposits, but rinse thoroughly, as it can corrode some fixtures and etch glaze on tiles. You can also try-tea tree oil -- 2 drops tea-tree oil with 1 cup water -- in a spray bottle. A natural antiseptic and fungicide, tea tree oil costs more than vinegar but will kill most types of mold and help prevent growth; as with all concentrated oils, it should be used with caution, as it can trigger allergic reactions if it comes into contact with skin.