One of the easiest changes you can make when planning a green wedding is to use eco-friendly alternatives to common items. For example, weddings use candles, and most candles are called "paraffin candles". Paraffin is a by-product of the oil industry, and it is petroleum based. Burning candles may smell nice, but it really has a negative impact on indoor air quality. There are two main alternatives: Beeswax and Soy.
Beeswax candles are natural, and often local - wherever you live, there is likely someone making beeswax candles. Many bee farmers gather the wax from the bee hive, and make it into candles. One Manitoba company that makes fantastic beeswax candles is Wild Dog Farms.
Another alternative, which I use regularly, are soy candles. Made from natural soybean wax, soy candles are very clean - they leave almost no soot, they wash off of fabric with warm water, and they don't burn as hot as paraffin candles. I use these candles because they are eco-friendly, but they also have a practical side - one tea light candle can burn for almost twice as long as a paraffin tea light candle. From an event planners perspective, this means I don't have to run around lighting candles so often. The candles will not burn out by the first speech - they will last well into the night. I like Chinook candles, which are made in Alberta.
There is a good article on soy candles here.