Go to a nearby stone quary or gravel pit. I have done this a few times in the past and they didn't even charge me for the pea gravel. It is a natural look that I like. I have it in my 120 gallon and it is planted. They usually sell it by the ton or truck load so if you go in and tell them you need a couple bucket loads they will probably give it to you.
This isn't the best pic in the world but it will give you an idea of what it looks like.
