Ethanol - Can be produced from plant material so is know as a biofuel. It's made by fermentation of plants and is used to power cars in some places. It's often mixed with petrol to make a better fuel.
Pros: The carbon dioxide when it's burnt was taken in by the plant as it grew, so it's 'carbon neutral'. The only other product is water.
Cons: Engines need to be converted before they'll work with ethanol fuels. And ethanol fuel isn't widely available. There are worries that as demand for it increases farmers will switch from growing food crops to frowning crops to make ethanol - this will increase food prices.
Biodiesel - another type of biofuel. It can be produced from vegetable oils such as rapessed oil and soybean oil. Biodiesel can be mixed with ordinary diesel fuel and used to run a diesel engine.
Pros: Biodiesel is 'carbon neutral'. Engines don't need to be converted. It produces much less sulfur dioxide and 'particulates' than ordinary diesel or petrol.
Cons: We can't make enough to completely replace diesel. It's expensive to make. It could increase food prices.
Hydrogen Gas - used to power vehicles. You get the hydrogen from the electrolysis of water - there's plenty of water about but it take electrical energy to split it up. This energy can come from renewable source e.g. solar.
Pros: Hydrogen combines with oxygen in the air to firm just water - it's very clean.
Cons: You need a special, expensive engines and hydrogen isn't widely available. You still need to use energy from another source to make it. Also, hydrogen's hard to store.