I found this helpful little color wheel when I was looking around for inspiration on flowers and wedding colors. This can be used to find matching colors for your wedding.
You can choose colors from the same 'slice' and create a monochromatic scheme.
You can choose colors opposite to your primary color, or you could choose colors on either side of your primary color. These are the most common chocies, of course you can do as you like too =)
This video explains a bit more